HikaShop is an e-commerce solution for Joomla. They have a pretty usable free edition, and reasonably priced commercial editions with support.
We worked together with the Hikari team to make our Varnish-Joomla integration work with all editions of their extension. The result of this work is available in version 1.3.1 of our package, which was out in November 2013.
No matter if your shop receives thousands or millions of view every day, your prospective clients deserve fast page loads. Visitors who don't have anything in their cart will enjoy viewing pages from cache, and more server processing power will remain for these who actually need it (visitors with items in their carts, visitors doing checkouts, your staff). Everybody wins.