Despite the existence of a myth on the Internet that tipping is not accepted in Iceland. And also the myth that tips are included in the price of the dish. This is wrong.
Tipping is accepted and not included in the price.
Working with tourists is a big challenge, because 50 times a day waiters have to explain the same thing, talk about each dish, give recommendations in accordance with the preferences of the tourist, as well as the allergies of the tourist. So it's fair when that individual work is rewarded.
Also, the waiters make sure that the restaurant kitchen prepares the dish with exactly the exceptions and additions that the client wanted. This is a delicate work between restaurant visitors and the restaurant kitchen.