I just wanted to second the opinion to go early to Guest Services to do this and don't wait til the last night.
I charged my tips to the stateroom account a couple weeks ago. I went the day before the last day and I went in the middle of the day -- not around the dinner and breakfast rushes. It was great. They said since I was giving the recommended amount, they filled in the totals for me and gave me a receipt and tickets to give each person receiving tips with my name, their name and the amount. It was all done in about 1 minute.