I will admit I have never had a dog that needed a groomer until now. Is it customary to tip? I don't want to be a dick.

If yes how much for a small dog like a shit zoo

I do tip but our groomer also happens to be the breeder we got our dog from and she is always giving us stuff for free because he was one of her babies. We get free nail clippings and baths about every other month so we take pretty good care of her.

Just the tip

Generally, yes.  Most people do tip their dog groomers if they have any direct interaction with them.

I say "if you have any direct interaction with them" because some folks take their pets to chain places like "Pet Smart" where you might never actually meet or even see the actual "groomer".

I can't really recommend a typical percentage or anything because my wife takes care of all that with her (errm... I mean "our") punt puppy.  

I do love that critter but they're the gift that keeps on giving.  

If you are pleased with the work, yes.