Heating oil #2 vs. Diesel oil prices

Home heating oil #2 and diesel #2 are essentially the same with the key exception of road-tax. (Heating oil is dyed red to indicate no road tax.)
I recently received a fill-up of heating oil #2 at a price of $3.70/gallon from Woodford Oil. I also recently filled-up my car with diesel at Krogers for $3.75/gallon. The tax rate on diesel fuel for highway use includes a 50 cent per gallon tax, so I really paid $3.25/gallon for my diesel, a whopping 45 cents per gallon difference!

Seems to me Woodford is engaging in price gouging by selling at the price of road-taxed fuel, and pocketing the profits.