Help with tax rules Drupal Commerce when applying discount to order

As many people are aware the VAT rules in Europe are different to the US and Canada when applying tax to products and orders where discount is applied. Drupal Commerce by default shows the VAT on an order with discount applied as the original VAT amount.

I need the VAT to reflect the updated order total after applied discount and not the original VAT amount.
e.g
Cart total 100 SEK
Subtotal 80 SEK
Tax 20 SEK
Total 100 SEK

with discount applied of 10 SEK to cart total should be
Cart Total 90 SEK
Subtotal 72 SEK
Tax 18 SEK
Total 90 SEK

... and not the original Tax of 20 SEK which is what Drupal Commerce wants it to be.

I am aware that tax is calculated on the product and not the order total but surely there must be a way of correcting this.

Please quote for a solution.

Thanks