Diesel prices - truck stops vs regular gas stations

I was a truck driver about 15 years ago. I remember there being something different about the way tax was handled on diesel at the truck stops in Indiana. It was different than any other state I ran in.
I don't normally see that much difference in other states. Here in VA diesel at truck stops is often very similar to regular gas stations. Sometimes the truck stops are less by a few pennies, sometimes not.