TAX calculation incorrect

Hi. I’ve spent a couple of hours with your plugin and it looks like there’s a bug in the tax calculation.

Consider that in France the tax is 20%, the discount configured is 5% and the cart contains 1800 Euros of products without tax.

The order page describes the following :
Products : 1.800
Discount : -90 ( 1800*5/100 )
VAT : 360
Total : 2070
In this situation, the VAT is wrong. It should be (1800-90)*20/100 = 342 where as it is calculated on the price without the 5% discount.
So the total is wrong : it should be 1710+342 = 2052 (and not 1710+360 = 2070).

So let’s check the “Is taxable” option.
The order page describes the following :
Products : 1.800
Discount : -90 ( 1800*5/100 )
VAT : 342
Total : 2052
Nice ! The VAT and the Total are ok. So you think that this setting is the right one.

But now the things are getting more complex.
This time, the cart contains a book that costs 7,49 Euros without tax and in France, on the books, the VAT is 5,5%.
The order page describes the following :
Products : 7,49
Discount : -0,37 ( 7,49*5/100 rounded at 2 digits)
VAT 5.5% : 0,41 : incorrect because calculated on the full price and not in the discounted price, so should be 0,39
VAT 20% : -0,07 : a negative value calculated on the Discount “taxable” ( 0,37*20/100)
Total : 7,46 ( = 7,49-0,37+0,41-0,07) which is incorrect.

In the settings, you can select the VAT rate linked to the discount. But that schema does not handle the situation when the products are sold with different level of VAT rates in the country (and I don’t think that France is isolated in this situation).

Best regards.

Franck.

PS : I really spent hours to debug all these situations (and others) so please take a look at this issue so we can leverage the quality of the plugin.