it’s mildly annoying when a manga translation “translates” yen to usd (particularly when it’s not just a translators’ note and they put it in the actual panel with no mention of the original)
for one thing, you don’t know that all your english-speaking readers live in the usa (especially in the case of internet-published scanlation) but also… the exchange rate is not ever going to consistently be the same. don’t do this. if you really don’t think your readers will understand the concept of different currencies just put a translators’ note