Then surfing the extensions here, I happened upon the JooCommerce Shopping Cart. I purchased the package, downloaded it and installed it on my test site. Installation was easy as there are only 2 items to install. The Component and the shopping cart module. And you don't really don't have to install the shopping cart Mod as the Component is supplied with a cart.
It worked great, easy store set up, currency, Taxes, shipping. The UI looks great and it will work great on SmartPhones and other tablets. The only thing I can see that it needs is a percentage options available on in the shipping. Other other than that it's just a great program.
If you are looking for a simple effective, easy to use shopping system, I heartily recommend this program. Plus their support is excellence. You will not be disappointed.