The price is always shown in the shop currency. Just do not select the 21% rule.
So lets assume the setting is pricesbyCurrency=0, then it does not make sense to have prices in different currencies. This is for importers. For example a swizz shop buys in Dollar but sells most time to the EU, then he can use an own USD with fixed rate (when he bought it) and sell it with dynamic rate of CHF to EUR.
pricesbyCurrency=1 says, try to use the given currency, if not use the normal shop currency.
So back to the swizz shop (I wrote it actually for a swizz shop). The swizz shop added always two prices, one in CHF, one in EUR. The EUR price is always calculated the normal way. That means that you see the 29 euro recalculated back in Cz Krones. and the price is higher, because it looks like that you entered the EUR price as Brutto.
The swizz shop just wanted "nice prices" in both currencies (the 29,90 for example and not 29,87)