can't imaging anyone in the
can't imaging anyone in the "gas pump industry" would advise you to completely fill to the top of your tank. Not only a negligible difference in overall calculations it would lead to an environmental disaster if everyone were to do this.
I have been in the habit of calculation my MPG since my first car I owned (1972 Ford Galaxie 500) had a faulty gas gauge. I have had dozens of vehicles since then and still continue to this day. I have found most have been within 5% accurate some more accurate than others. My last BMW would give me ratings that were over around 10% it also had a speedometer that was 2 MPH fast (not sure if this is related) many forums also revealed BMW's to have optimistic speedometers but fairly accurate MPG gauges. On the other side my wife has a 2021 Mazda CX-5 that consistently gets better MPG than the meter shows. Back to the reason I replied to this post, DO NOT TOP OFF your tanks please. This not only contributes to ground pollution buy vapor release into the environment. It may seem like a small thing but when practiced millions of times per day this is a very bad idea!! There is a reason they have auto-stop AND vapor collection on fuel pumps.