Discount after Tax

Hello Guys,

im currently working on a shop for a client in Germany. After making the most work flawlessly i am struggling a little with discounts. The actual calculation works pretty good if you use it before tax. But in Germany its more common to apply discounts after tax. For Example you have a product that costs 100€. The tax is 19% which means the grand total is 119€. If i now add an discount, lets say of 15€, the user expects the total price to be 104€. Instead Perch is calculating before tax which makes the price 101,15€.

Is there any "easy" way to apply discout after tax?

I know that i could my own calculation in the template. But this doesnt seem to be a clean solution for me.

Thanks in advance, Bastian