Credit Card currency conversion fees

@mattia says:

tumbleweed: one thing that in my mind is not clear how to properly write down: my receipt are in several currencies, but I paid EUR for all of them, including whatever fee my credit card took. besides writing down the original amount in the description and EUR in the amount field, how would you see this done?

We could track this. I could imagine having a separate receipt total and charged amount (in different currencies) and some sort of limit on the conversion factor (e.g. $5 + amount * 10%)