when I see this I usually go custom and see if I can enter negative numbers.
I like how some PoS systems shame people into tipping. We need those here, especially in Cape Town.
Otherwise I generally tip 10% rounded to the nearest 10.
If it's a company card then 20 rounded to the nearest 10 or 100.
It also depends how the tip is distributed, i.e. is it only to the waiter or distributed to everyone including backend kitchen staff.
If something small like a coffee then 0 tip but a thank you to the staff.

would be the minimum