Whenever I see cops in the gas-station (which is most mornings) they always buy coffee and doughnuts. The cashier always says its on the house

Now I wonder why this is, are the cashiers trying to ensure that any future run-in with the cops will be in their favour. Or, is the gas-station owner running an illegal business 'out-back' and this is his fee for not getting busted (cheap

)?
Also, why do cops love doughnuts so much?
Do they have to have annual physical stamina/physical tests? Cos the ones I see are VERY large, and look like they have had one to many doughnuts :-3