I'm running an eCommerce website that allows users to select their preferred currency via a drop-down in their shopping cart. The currencies are localized using real-time exchange rates from a JSON API and are pretty accurate, but not guaranteed.
My payment processing system only allows incoming payments to be in Canadian currency and I make sure to explain this to users in my FAQ - the localized currency is simply for comparison purposes.
With that said, would it make sense to show everything leading up to that final checkout in their localized currency (should they choose it from the dropdown) and then send out the final receipt showing Canadian currency? At the end of the day, I don't really know the exact amount that the users payed in their local currency nor do I know the exchange fee that the bank charges to convert it to Canadian.