$.50: almost always they may laugh or just think you accidentally taped it on.
$1.00: once you start getting into bills it gets a bit more serious. Your teacher will start to consider if they know what you mean.
$5.00: now you are past the joke and are a bit more serious. If you are on the border line they may raise your grade but no promises.
$10-$20: This is just pointless because their is no need to waste this money, also they'll probably just give it back.
Most of the time to use this method is when you want
to try to make your teacher laugh. On rare occasions will it ever increase
your grade.(Similar to gambling)