Unable to calculate VAT correctly

Hello, I was unable to find a solution for the following issue:

Example: A products costs 81.25 (the price includes 20% VAT, in other words, 67.71+13.54 ). Within Shopping Cart, we'd see the following break-down:

Sub-total: 67.71 (that is price without VAT)
+20% VAT: 13.54 (that is the VAT, achieved through Taxes)
-10% Discount: -8.13 (all products over $50 receive 10% discount, that is, 10% off of 81.25)
TOTAL: 73.12

Unfortunately, our customers are very sensitive to VAT, so the calculation should break-down to:

-10% discount: 8.12 (that is 10% off the full price of 81.25)
Sub-total: 60.94 (that would be the full price,81.25, minus the 10% discount or 8.12 first and excluding the 20% VAT second)
+20% VAT: 12.19
TOTAL: 73.12

As you can see, the Total is the same, but the VAT is different. I've tried a different Total Order from the OpenCart admin, but if I start with Discount, it does not have a previous value to discount in the first place and returns 0.

I would really appreciate your ideas.

I have now come to a possible theoretical solution, which I cannot apply in practice

Perhaps, the TOTAL part of Order Totals can be duplicated. Then, we'd have:

Full Price (that is Total 1) = 81.25
-10% Discount = 8.12
Sub-total (that is Price without VAT) = 60.94
+ 20% VAT = 12.19
TOTAL (that is Total 2) = 73.12

Tried to duplicate the Total part, but without success

I have a problem with it as well.

Total is OK, while VAT amount after discount is not OK.
So, we only need the VAT amount to be correctly displayed.

Your first example should adjusted like this:

1. SUB-TOTAL: 67.71 (price w/o VAT)
2. -10% DISCOUNT: 6.771 (discount)
3. NET PRICE AFTER DISCOUNT: 60.939
4. + 20% VAT: 12.1878
5. TOTAL: 73.1268

So,not doubling totals, what is important is the time the disount is applied... BEFORE TAXATION.

Anyone with a ready-made solution?

You need to fix the sort order for your Order Totals

Sub Total sort order 1
Discounts sort order 2
tax sort order 3
total sort order 4

Extensions > Order Totals