But it must be optimized. What will happen if 10 people win 200% of their bet?
The server account would be empty and the server will not be able to payout the winning values.
What about:
0-50: LOSE
51-69: 5% of Jackpot
70-80: 10% of Jackpot
80-90: 25% of Jackpot
91-99: 50% of Jackpot
100 : JACKPOT!
In that case the winnig profit is bind to the server's account balance.
and btw: Lucker! +1 win to your account
Er... "breaking the bank" is a risk that you, the "house" have to take. That's why we allow you to take vigorish (transaction fees). If you're worried about your risk, look at how Keno pays out, or roulette, or craps. Depending on how much risk you want to take as the "house" you can choose which sort of weights you want on winnings. Craps has the lowest payouts for the house, keno the most (13 cents on 100 dollars for craps, 13+ dollars on a hundred dollars for keno)
If you need some help setting your tiered bets up properly i might be able to help you, as long as you don't screw the algorithm up i'd recommend having about 10-100 times more than the maximum bet amount in your "house bank" to ride out statistical anomalies. It'll all work out in the houses favor in the end (and should, since they're paying the bills) - but it can get real choppy if luck goes to your players for a dozen hands :-)