The question has just been answered (2down) .
Sorry misread your question. Whether you submit your credit card or not, you can still pay at the end of cruise in USD. The'desk' is open 24/7 so after your last drink/spend you can go & pay.
We were on this ship in may pay in as many dollars to your account at the begining of the cruise as you like but better to pay in sterling as rate on the ship was better than the travel agents etc 2.2 dollars to the pound .