OpenCart is a great free, open source PHP cart software. Unfortunately it’s quite behind in terms of SEO. A default installation will end up flooding Google’s index with many duplicate category, index, and information pages which will dilute your search result positioning, hide your links in the duplicate content search, and possibly cause a “thin” pages penalty for having many duplicate low-content pages on your site.
Not to fear, this simple add-on will correct these shortcomings by addding canonical links to your category pages, your site’s main page, and all information pages. In addition, it will correct the “duplicate” index problem where multiple URLs point to the site’s home (an SEO no-no).
Installation is easy and the script comes with full instructions.