Gas stations have to be inspected every two years, I think. If the OP thinks their pumps aren't accurate, just call and ask that the station be inspected.

That being said, my owner's manual and all of the specs on my car say the tank is 15 gallons but one time I wasn't paying attention and ran out of gas. I put 1 gallon in a can and put it in, then drove about a block and put 15.4 gallons in without topping off. I think gas tank specs are kind of like the strike zone: rather approximate.