Trouble with this is the carriers won't be able to run national ads with their pricing. Instead the price will have to be concealed until you're about to sign up. Some states (Nevada) you pay around 7%, whereas others (I think NY?) it's 25%.
If it were purely taxes that the company must collect and hand over based purely on what you pay, I could agree with that, but when it is nebulous "fees" that are really cost of doing business that the company incurs, it's not reasonable. Furthermore, some of the fees relate to Federal fees that are the same in all states.
In the example I was quoting (renting a car at an airport), the company has enough information to quote the exact price with all fees at the time of booking.