Actually, I've done both. I purposely overpay a local restaurant that seems to be struggling and told them they should charge more. This isn't tipping a waiter, I get takeout and tip the store itself. And I've paid extra federal income taxes for several years by purposefully failing to take some deductions I'm entitled to and could easily substantiate.

This year I purposefully overpaid my business privilege tax to the township as well, and paid a special zoning fee for having a home office that I know my neighbors (who also have home offices) don't bother reporting and paying. I also donate money exclusively to organizations that are not registered charities even though donating the same money to a charity would net me cash back in taxes.

90% of people may rarely go out of their way to pay more than they have to, but it's not unheard of.