A product priced at $19.99 converted automatically to another currency rarely lands on a "clean" psychological price point in that currency. Manual currency-specific pricing rules, not pure exchange-rate conversion, usually perform better and need setting up deliberately.
Discount apps, subscription apps, and loyalty apps built before multi-currency was common sometimes calculate against the store's base currency regardless of what the customer sees — creating a mismatch between the displayed price and what actually gets charged or discounted.
Some markets expect tax-inclusive pricing shown upfront, others expect it added at checkout, and getting this wrong by market creates both a compliance risk and a trust problem at the exact moment someone's deciding whether to complete a purchase.