When we were on one of the Iceland/Norway sailings, by the end of the trip we had a small amount of various currencies left over. Our bank at home charges a flat fee per currency to make an exchange and it really wasn't worth it for the small amount that we had left over. So went to guest services on the last day of the cruise to see if they would apply it to our on board account. It was no problem at all. I have no clue if the exchange rate was comparable to what a bank would have given us, but they did not charge us a fee, so it probably came out just as good (or better) than what we would have gotten from our bank at home. We didn't ask for cash back, but just applied it towards our on board account balance. Super easy.