Is it a dollar, 4 quarters or 10 dines?

Crystal, Seabourn, Siverseas, and Regent 7 Seas have the main tips included. Do you really think you have not paid them when you paid your fare? Regent 7 Seas had an auction for fun "job rights", tending bar, interviewing an employee on their tv, eating with the chef...to raise money for the crew funds in addition. Totally optional.

Holland American and Celebrity charge an amount PP/PD dependent on cabin level to your bill. Holland allows a clawback if you disagree with the amount OR you can add more. Some clawback a portion and distribute in a manor they decide versus the way HAL might choose. Several years back HAL passed out envelopes and you did as you chose, although they did give recommendations.

As far as tips, generally these end up on your bill. Tips on board that you choose to hand to someone, normally would be in the currency of the ship, most often US $s.

Not mentioned, but for budgeting, don't forget shore excursions. When possible this should be in local currency. US$'s often ok otherwise. No coins, as they are very had to turn into local currency. Depending on your travel plans, there might be the hotel, taxi, bus to the ship, etc. Some of these may or may not be include in your fare. Read the brochure or docs. In Tahiti, don't try to pay Le Truck in US$s. The driver will cuss you out. OOps, guess I should have asked in advance.