Rolling 1 or 100 = 4x payout, chance of 2/100
Rolling 85-90 = 3x payout, chance of 6/100
Rolling 65-80 = 2x payout, chance of 16/100
Now, if the player makes a 1g bet, he has the following outcomes:
His chances of losing 1g = 76/100
Chances of gaining 2g = 16/100
Chances of gaining 3g = 6/100
Chances of gaining 4g = 2/100
So the player has an Expected Value of -1*76/100 +2*16/100 +3*6/100 +4*2/100 = -76/100 +32/100 +18/100 +8/100 = -18/100 = -.18
This means that the player may expect to lose about .18g for every 1g he bets, 1.8g for every 10g bet, 18g for every 100g bet, etc. A profit margin, for you, of +18%.