What do you tip at the salon?

I’ve always wondered what others tip at the salon. I tip 20 percent usually, but because I get cut, highlights and sometimes even other services my price can be high. I spent 6 hours in the salon today and the price came out to 420 because I did a whole revamp, highlights, toner, clarifier, wash, cut, blowout, the works. I knew the pricing when I went in bc it was given to me up front and tipped 20 percent which was about 85 dollars. I feel good about that, but my one friend always tells me tipping that much on an already very high price service is too much. Paying 500 for hair is high but I don’t get it done often. Just wondering what other people do.