How much to tip?

How much should you tip a piercer? I got my nose pierced and had no idea how much to tip for it. The cost of the piercing was 30$ plus the cost of jewelry, so it ended up being 45$ and some change. I gave him a 50$, he gave me 4 dollars and come change. I gave the piercer those four dollars plus the 5$ I had set aside for the tip. But I didn’t have another dollar to make it an even 10$ (what I wanted to tip), so I tipped her 9$. Is that bad? Or is it okay?