Making change.

I got this in an email from a close friend. It is definitely a great problem.

"After our fb discussion on young people not able to make change, my daily warm up questions for my math 1 class next week are all of the following sort:
Susan's total for a pack of gum is $1.27. She hands the cashier $2.02. Why didn't Susan just give the cashier $2? What is Susan's change?"

Thanks Leah!