I took a few moments to look at Cubecart V4 as recommended by "node-net", and I agree that, at first glance, it seems to be a nice cart composed using CSS.
Having not ever used it though I have had extreme success with Early Impacts Shopping Cart. It is also composed using CSS and if you know how to navigate ASP includes and external style sheets you can customize it to whatever your site design is instead of using the cart defaults that most shopping carts give you. Good Luck with your new business!!

Saxman -