Grand Total in Checkout

Hello everyone,

On the last step of the checkout, I have grand total sum of: 170 euros that is correct. That sum is calculated as Product Prices x 19% VAT plus shipping costs. But, when as a customer I am trying to pay the grand total, it’s different because of the fact that Grand Total is calculated as Product Prices x Default VAT (20%).

In my case I have different VAT for specific country and am using my own functions that calculating netto prices x VAT.

Also, when I am doing this:
var_dump($oBasket = $oUser->getSession()->getBasket());
I can see that OXID is using _dBrutto variable for getting Grand Total Price, and not my variable grandTotal.

Any suggestion how to change _dBrutto or set my variable grandTotal as valid?

Thank you.