My F150 has the "gallons used" meter, and it's typically about .1 to .3 lower than the pumps on fillups. It's also been 'bang on' a couple of times compared to the pump gallons.
On my last camping trip of over 650 total miles and some 53 some odd gallons of gas (going by memory now, but I calculated it at home), the total amount the meter was off from the pumps was .3 less than the tickets.
Good enough for my books! I don't bother to keep record of it anymore and just go with the meter and just compare at fillups. As long as it remains constant I'm going with the meter.. If it starts getting more than 1 gallon off, then I'll re consider..
Your mileage may vary.. :)
Mitch