Truthfully, I sort of think of $20 as a price point. Of course, that's a cash layout. Some street vendor offers me something I want but value at $17. "Yeah, whatever, here's a $20." If he's selling it for $22, I probably just pass because that requires too much work. A 20 and 5 while fully expecting him to say "Sorry, dude, I don't got no change" after I hand him the $25. I sure it doesn't work exactly that way on the internet with a credit card but I still fill up my truck with an round number if I can despite not paying cash for fuel in 15 years.