Let me choose whether the discount applies before or after tax

I need to be able to choose whether a discount is applied before tax or after tax. Right now MonuDesk always applies the discount before tax, which lowers the taxable amount. I book my discounts after tax in QuickBooks, so on a recent order a $75 discount created about a $5 difference between MonuDesk and QuickBooks because the taxable base didn't match. QuickBooks lets me pick before-tax or after-tax. I need MonuDesk to let me pick too, so my numbers reconcile and I'm not fixing cent-level differences by hand.