From Oregon DEQ (Dept of Environmental Quality) website:

"Oregon law now prohibits topping off vehicle fuel tanks during refueling.
Topping off causes gasoline drips and spills that release harmful pollution,
wastes fuel, and causes vapor recovery equipment in vehicles and at gas
pumps to malfunction."

I suspect many states have similar laws, of course in Oregon fuel is
despensed by highly-trained, expert fueling technicians.

Regards,  Vern