So our owner made up a new way to do commissions, and it's taking me four days to manually calculate them and to be honest, I'm so afraid of human error, it's going to catch up at some point, so I'm hoping there is some sort of formula that can help!

Our sales team gets a percentage based off the profit margin range, and I need a formula that can meet 8 conditions - which is where the "IF" conditions fail me.

Basically all my "IF's" are:
0-4 = 0%
5-10 = 5%
11-15 = 7%
16-19 = 9%
20-23 = 10%
24-27 = 11%
28-33 = 13%
34-37 = 14%
38-100 = 21%

And that percentage times another field yields their commission.

Help please??