The closest to that I have seen was a terminal in Alaska (or Canada, not sure) which had a option to add a percentage. Had to do a bit of mental math to figure out the right percentage to end up at a nice round number :)

I've certainly never seen an option like that in NL. The three common things I see here are 1) you say "make it amount X" before staff enters the amount in the terminal, 2) you leave some extra cash on the table after paying the normal amount with your card, 3) just don't tip (which is acceptable here since wages are decent enough).