Not Tax on 2nd product

Hello when i try to buy a product from my site the tax isn't working correctly. When i add the first product the tax is calculated in the cart correctly but when i add a 2nd product to the cart the tax is not showing in the cart as well. When i do a complete checkout it is still not showing correctly. Anybody got an idea what's going on?

Lets start off with Version of OC you are using.

Is there any custom modules installed or core OC functionality ? your store url ? .