I'm going to use PC to rentout products. It is common to state the prices without tax and then add the tax on the summary page (orderverify).

Thus, it would look something like this:

Product 1: $50
Product 2: $50
-------------------------------
Subtotal: $100
19% Tax: $19
Total: %119

Is this possible (maybe with some kind of mod)?

That is the way the system works, unless you are using VAT, in which case ProductCart assumes that the VAT is included in the prices displayed on the store (see the User Guide for details).

If you are using VAT, but want to add it on the order verification page, then things get tricky because in the same order you might have products that have VAT included already and other products that do not. That scenario is not supported.

Yess! It is possible.

What I did is have input all prices as excl. VAT prices. Then I added a tax regon for a specific country. As the cart is set to only use one country it's no problem. Now I tell the cart to add 19% and show it on the verify page. And voila! It works exactly like I want it too.