Promotions to be calculated on total with TAX

We are looking to have the Promotion dollar value “BY FIXED AMOUNT”
to be done after the TAX and SHIPPING have been calculated
I tried a few different Hooks and they have all failed. Anyone know where in the code I can make the change so that the promotions come off the TOTAL (Product + TAX plus Shipping if Any) then MINUS the PROMOTION and the balance showing This is for 4.17.2 it worked perfectly in 4.12 CS-Cart Ultimate B2B