Hello, OP here. Thanks for all the responses, everybody.

I'm surprised there is a consensus that you should not modify tips according to state law. This type of consensus is very rare on Flyertalk! Here is the reasoning that led me to ask this question:

First things first, I hate the custom of tipping and I wish it would go away. But I realize that it is reality. In most cases, states assume that certain workers will receive a certain amount of tips, and modify their labor laws accordingly for those workers. Therefore, despite my dislike of the system, if I don't tip then I am cheating these workers of their wages.

However, in states that do not have a lower minimum wage for tipped employees, this logic no longer holds. Servers are entitled to the same wages and benefits as untipped workers. If a cashier can get by on this salary, it should be "enough" for this type of work. Therefore, by not tipping, I am not cheating anyone of their wages. Tips for these workers are a bonus, as they should be.

Based on this logic, over the last year or so I have started tipping less (around 10-15%) when traveling in the states I listed in the OP, and more (20-25%) in the rest of the country. When the minimum wage for restaurant workers ranges all the way from $2.13 to over $9, I think this is fair.