Once I handed a $20 bill to a cab driver and told him to "keep the change" and he falsified a receipt. Thanks, but I'm going to tip through the normal tipping

Once I handed a $20 bill to a cab driver and told him to "keep the change" and he falsified a receipt. Thanks, but I'm going to tip through the normal tipping mechanism with my normal payment method to ensure that everyone stays honest. And that probably includes the honest GrubHub drivers who invariably ditch my drink if they decide I haven't tipped high enough in the app.