Fun topic! In my travels, I've discovered that the locals in those countries that claim they don't tip ALWAYS tip but then have excuses for why it isn't actually a tip. The drink offer where the bartender just pockets the money is a perfect example of this.
I've seen rounding up and leaving the change to be common (or leaving some loose change from your pocket if you pay by card). When I was doing most of my traveling, I recall the exchange rate being something like $1.50-2.00 per one pound or euro so this could add up to a decent amount. On top of that, a lot of places will automatically add a "service charge" (i.e. a default minimum tip) in the 10-15% territory. Once you add that service charge to the change, you end up paying at least the conventional US tip of 15-20% (but just don't call that a tip!).
The horrible thing about this is that it is common advice for popular guide books, travel sites, etc. to say these countries don't tip and you shouldn't tip when this is often flat out not true.