I keep a mental note of the stations in my area on the price of Diesel. If I have to drive more than 10 minutes in traffic to save a nickle to 10 cents more then the $1.00 to $2.00 I saved on a twenty two gallon fill up isn't worth it as I used that much gas to get there.
That way if I am getting below a 1/2 tank then I will stop and fill if that station is that much cheaper than near my house.
I filled up in MD yesterday at 2.79 for 87. I noticed when I got bavk into WV it was 2.89. Our taxes are a little higher on gas here. But less on most other things. It was probably cheaper in VA but I wasn't headed that way.