What is considered a reasonable tip for a $12 haircut?

I usually get my haircut at Great Clips and the cut is $12. I have never really known what the stylist considered a good tip. Does the 15%-20% rule still apply? I would like to hear from people that work in one of these places.What is considered a reasonable tip for a $12 haircut?
20% is standard today. i'd round up and give her $3What is considered a reasonable tip for a $12 haircut?
my auntie works in a hair salon and most of their cuts are like $13 she says a good tip is like $2 - $3!