Nested IF formula for sliding commission scale

I am trying to create a sliding commission scale where the following occurs:

The formula will be in Cell E45 and need to return a value of "0", "6%", "8%", "10%" based on Gross profit Percentage.
Gross profit is cell I50

Example if Gross Profit is less than 50%, then 0 commission.
If Gross Profit is 50-60%, then 6% commission
If Gross Profit is 60-70% then 8% commission
If Gross Profit is 70% and greater then 10% commission.

I have come up with the below formula but unable to get that last statement to work once a gross profit of 70% or more is reached.

=IF(I50<50%,"0",IF(I50<=60%,"6%",IF(I50>=60%-69%,"8%",IF(I50>=70%,"10%"))))

Does anyone have an suggestions on the correct formula?