Spare Change Lottery

I hate change. The coinage sort, I mean. Whenever I get change, I always drop it in the tip jar or the milk fund or the hand of the next person in line.

Many supermarkets have little electronic pay-with-yer-credit-card lottery stations at checkout stands now. I propose a different sort.

You drop your coins in, and based on the amount you've paid it instantly calculates your chances of winning a $5 prize, $10 prize, or $20 prize. Then it chooses a random number and--if you're lucky--spits out a bill. Simple as that. Winners would be fairly frequent.

One disadvantage: less money for the milk funds. Then again, if the gains go toward education, it might be for the better.

-----EDIT FOR CLARITY-----

I shouldn't have called it a lottery. There are a few significant differences. *This* system returns immediate positive reinforcement, requires no ticket or time, and works solely on a small scale. You are not in a "competition." (Jackpots need to be done in a lottery format because the number of winners needs to be very carefully controlled.)

So I'll make this idea more concrete: At the checkout, there's a little box with a coin slot on top designed for dumping a fistful of change (like on some public transit systems). You dump your change. It counts your change, multiplies the amount in cents by (e.g.) 0.16 (let's call the result x), randomly generates a rational number between 0 and 100 (y), and, if x>y, instantly spits a fiver out a slot. Boom. Done. Thank you for playing.

If the average amount dumped was 50c, 8% (!) of customers would win, and the machine would make 20%.

And, yes, if you gave $6.25 or more, you would automatically get the $5.

---------------