We have a similar problem in the UK with Scottish bank notes. They're legal tender across the whole of the UK, but most shops in England have never seen them before.
Thanks for sharing these links. I think the second video was the most enlightening. Even the security guard had the insight to think "why would someone fake a $2 bill?".
But because of quarters you still probably need nickels.
Or you could just go binary use halves, quarters and eighths.