Although there are dozens of threads on tipping, I just wanted to thank you for an Aussie starting one. Most of these threads are started by Americans, and at some point in the thread someone points out "well, there are places like Australia and much of Europe where tipping is not common, and [insert some argument for or against tipping here]." I think you have the right idea: Do whatever is most common in the place you're visiting, and if you don't know what is common, then ask (as you are here). For all or most of the Caribbean, American-style tipping is probably the right course. As for the specific amount to tip, I think that's been well covered. Enjoy your trip!
My in-laws come from a non-tipping culture, and I've seen them struggle with it when they visit us here in the US. It can be stressful to have to think about not forgetting the tip and embarrassing when you do. Don't let it stress you out.
