I took Canadian but brought some US one dollar bills for tipping.
In-terms of tipping though - go to a dollar store and buy gifts to use to tip with. I brought a load of little things with me - pens and pencils, notebooks, stickers, gum and candy, travel sized toiletries, hair clips and elastics, lipstick....
The maids definitely took extra-good care of me because of the gifts I left each day.
I remember this one girl who was working in one of the restaurants at my resort... She seemed very young to be working - she could barely speak English but she was trying so hard to have a conversation with me. Super-sweet girl who was in school.
I wanted to give her something so I told her to wait while I ran to my room. I grabbed a pile of school supplies that I had brought and a bunch of coloured barrettes and earings. She was so grateful. The next day I was walking around the resort and I ran into her. When she ran up to say hello, I couldn't stop smiling..... She was wearing the earings and all those little, mismatched barrettes I had given her the night-before. It looked a little silly lol but so cute.... It was one of those moments when I realized how lucky we are in Canada... and how a little bit of kindness can do so much for someone who has very little.