Add a Tip after the Total and Coupon

I am trying to do the following calculations, but since there is only one Total field, the Coupon % gets taken off of the total AFTER the Tip.

What I want:
Subtotal Total - Coupon 10% = Total
Total + Tip = Grand Total

What is happening:
Subtotal Total + Tip = Total
Total - Coupon 10% = Grand Total

Is there a way around this that I am not thinking of?

Thanks, Sheri