I usually got with around 50 or so. It also depends on the cost of the tattoo and whether or not you'll be going back. The first time I ever went to my current artist, I really liked the quality of the tattoo, so I tipped her well. The same thing the 2nd time I went. Now when I go, the front desk guy will give me an "estimate" on the tattoo price. Then I go to the back to start the session, my artist sees it's me, and she drops the price for me (this has happened exactly like I said above 3 times now). If you want to be taken care of next time, tip well.