Tax Calculation

[K&K media production]

Or if you want that vm calculates the cost price on the fly, I've a plugin for this.

With this Plugin this is the workaround:

configured product cost price: 10
configured product final price: 10
configured vat rule: 22%

prices on frontend for your customer:

cost price: 8,20
vat 22%: 1,80
final price: 10