I used euros or pounds when I flew to Europe. The drivers always seemed happy.

Now that I fly to Latin America (various countries) I don’t carry local cash. I tip in greenbacks. Again, the drivers always seem happy.

One place you never want to tip is Japan. It’s an insult. I hope that one day the rest of the world is the same, but in the meantime I’m not going to fight the good fight to try to change the world, unlike some on this thread.