What states charge sales tax on gasoline. I’ve traveled in all 50 of them and don’t ever remember paying more inside than it says on the pump.
It’s been mentioned here that in IL there are sales taxes on gas.
http://illinoishomepage.net/fulltext/?nxd_id=245117
mentions there are 7 states that charge a sales tax. You likely have not noticed this because the sales tax is included in the price per gallon at the pump.