This app is as fast as convenient, as easy as useful:
ECBCurrencies offers a list of more than 30 currencies, with their exchange rates updated regularly from the servers of the European Central Bank (ECB)
Out of these currencies you can choose one as the reference currency. Additionally you can choose as many favourites as you like that are displayed in the section below.
Just tap on any currency, and you can perform any calculations of that currency in relation to your reference currency.
No more standing in a tourist gift shop and guessing helplessly the cost of some nice souvenir ...