Jane to whom are you replying in the last message? Are you traveling alone? Ten Dollars per day per traveler. So if there are two of you it is $20 a day.
The crew serving you makes there salary from the tips, they are paid almost NOTHING by the cruiseline. TIpping IS an expected part of cruising expense.
as for it being added to your account and paying that account. Most people put down a credit card to cover that account when they board the ship all onboard charges, drinks, soda, purchases, excustions and tips are charged to that card on the last day. You then have whatever time your credit card company gives you to pay it off.