Why are discounts applied on gross prices and not on net prices?

[dpomt]

Hi,
my customers shop only display net prices. The tax is only added on the total net sum to get the total gross sum.

I have debugged and noticed that the ShoppingCartLineViewModel Lines are kept as net prices (what I have expected) - but only until tax is provided (excerpt from original OCC source code):

I do not understand the comment that unit price and line prices need to be set to gross prices as base of promotions.
For my customers secenario, account is applied on net unit price.
With the given implementation basing on gross prices, I am getting discrepancies in price calcuation.

Example:
Before tax is applied, cart (lines in viewmodel) looks like:

After applying tax net prices are switched to gross prices:

And after applying discount 3% on item on gross prices:

What I need and was expecting to get is the discount applied on net prices:

As you can see, the prices sums/tax differ.

Any ideas how this could be solved? IMO discount should always be applied on net price and hence applying tax should not change net price to gross price in cart viewmodel lines.

[dpomt]

I have locally changed the implementation to fit my needs: keep net price in cart instead of changing it to the gross price.
Maybe the standard implementation could be changed somehow similiarily.

I have changed this:

1. Events/TaxShoppingCartEvents.cs
   DisplayingAsync: don’t override cart items NetPrice with GrossPrice

2. Events/PromotionShoppingCartEvents.cs
   DisplayingAsync: Instead of calculate NetPrice from GrossPrice now calculate GrossPrice from NetPrice

3. Payment/Services/PaymentService.cs
   CreateCheckoutViewModelAsync:
   i) Calculate grossTotal from netTotal (hardcoded :( - would be great to have applied tax ratio in CheckoutViewModel to access it here)
   ii) Pass grossTotal instead of total as second parameter to the CheckoutViewModel constructor

screenshots:
1)