Converting 39.90 euros into zlotys gives 171.43. The amount is exact, it is unreadable, and it immediately signals to the Polish customer that they are buying on a foreign site whose prices were converted automatically.
Price endings are a cultural and commercial convention, not a calculation result.
Why endings matter
Two distinct effects, and the second is the most important in an international context.
The perception effect. A price ending in 9 is perceived as belonging to the lower ten. The effect has been documented for a long time, it is modest but real, and it varies by category.
The credibility effect. This is the one that counts here. A round price, or one rounded according to local usage, looks decided. A price with three apparent decimals looks machine-calculated, and it casts doubt on the merchant’s command of that market.
A third, less known effect: on some segments, the round price works better than the 9-ending price. Luxury, craft and high-end services use round prices because they signal assumed value rather than optimisation.
Conventions are not universal
The point that decides the configuration, and one that is almost always ignored.
The 99 ending is widespread in Western Europe and North America. It is not the norm everywhere.
Several markets favour other conventions: endings in 90 or 95 in some European countries, round prices elsewhere, and on some Asian markets digits considered favourable or unfavourable according to the local culture.
The practical rule: do not transpose your home-market convention onto every market. Look at what local players in your sector do, that is the best source.
Technical corollary: your rounding rule must be configurable per currency or per country, not global.
The conversion problem
Three ways to handle the price in another currency, with very different consequences.
Conversion at the daily rate. The price changes every day, it is unreadable, and it makes any communication impossible. Reserve it for currencies that are truly marginal for you.
Conversion with rounding. The rate applies, then a rounding rule brings the price back to a clean ending. It is the most common compromise and it works well provided the rate is frozen over a period.
The price set manually per currency. You decide that a product is worth 39.90 euros and 179 zlotys, with no arithmetic link. This is what established brands do on multiple markets, and it is the only way to hold a locally consistent price positioning.
On a large catalog, the third model is unrealistic manually. The workable solution: conversion with rounding applied in bulk, then manual correction on the main references.
Price by Country, Shop & CurrencyThe right price displayed in every country, combinations included€89.00
The frozen rate and its revision
A management point that protects your margin.
An exchange rate applied live exposes your prices to daily variations. A frozen rate stabilises them but creates a gap with the market.
The common practice: freeze the rate, with a safety margin of 3 to 5% that absorbs normal variations, and revise it at a defined interval, quarterly or half-yearly.
Two complementary rules. Plan an exceptional revision if the gap with the real rate exceeds a threshold, 10% for example. And document the date of the last applied rate, otherwise nobody will know on what basis your foreign prices were built.
The effect on margin
This is what setting up rounding makes people forget, and it can be calculated.
Rounding down costs margin. Rounding up gains some, at the cost of a slightly degraded positioning.
On a catalog of a thousand references, systematic downward rounding of an average amount of 0.40 euro on an average basket of 60 euros represents about 0.7% of revenue. On a net margin of 8%, that is close to a tenth of the result.
Three calibration options. Rounding to the nearest, which statistically balances gains and losses. Systematic rounding up, which protects margin. Or rounding up with a cap, which forbids a gap above a given amount.
The second option is the easiest to defend internationally: the converted price is already an approximation, and rounding up compensates for exchange rate risk.
The VAT case
A frequent technical difficulty, rarely anticipated.
If you apply destination VAT rates, the same net price produces different gross prices per country. Rounding the displayed price therefore means working on the gross amount, which makes the net amount irregular.
Two approaches. Round the gross price and let the net fall where it may: the customer sees a clean price, your accounting handles amounts with three decimals, which is not a problem in itself.
Or round the net price and leave the gross irregular: your accounting is clean, the display less so.
On a consumer store, the first is preferable: it is the displayed price that is seen and compared.
What to check after applying
Four checks, to run on a sample before processing the whole catalog.
Low prices. Rounding calibrated on two-digit prices produces aberrations on small amounts. A product at 1.20 euro rounded to 1.99 takes a 65% increase.
Promotional prices. Should the rounding apply to the discounted price? If you announce a 30% discount and the rounding brings it back to 27%, the announcement becomes inaccurate.
Quantity-based prices. A tiered price rounded at each tier can produce inconsistencies, with a unit price that goes up at the higher tier.
Shipping costs. They follow the same conversion logic and also deserve rounding, otherwise you display a clean total with a shipping line at 4.73.
Display consistency
Last point, often neglected: the rounded price must appear everywhere identically.
Listing, product page, cart, order summary, confirmation email and invoice must display the same amount. A one-cent gap between the cart and the invoice, due to a rounding applied in one place and not another, produces complaints and complicates accounting reconciliation.
The check is done by placing a complete order and comparing the amounts at each step. Five minutes, and it immediately reveals calculation inconsistencies.
The Price per Country, Store and Currency module handles this chain on PrestaShop 8 and 9: rounding rules configurable per currency and per country, bulk application with preview, frozen rate with controlled revision and display consistency from catalog to cart and order documents.
