The formula for calculating the VAT [price * qty * rate / (100 + rate)] is wrong, isn't it?

You must replace the line
+= $item->price * $item->qty * $rate / (100 + $rate);
with
+= $item->price * $item->qty * $rate / (100);

I will also try to add some more features to the Module in the next few days. But I'm just a silly noob in programming drupal modules, so please be patient (and hope the weather will be bad, so that I have the time to read those drupalbooks)

And before I start coding: Is this the only module for displaying VAT? I don't want to do needless work.

greetings from germany!

EDIT: Sorry, that was wrong... Calculation is right, cause you calculate the vat IN the price.