Hi Ron,

as a sitemap generator JSitemap prevents automatically the inclusion of the same doubled link.

However if you have multiple different links to the same content the problem is different. To eliminate that you need to take care to have only 1 link/product in your Joomla website or as an alternative switch to an extension such as sh404sef to have an URL rewriting.
JSitemap has nothing to do with this aspect, moreover removing a link from the sitemap and still having it on the website would not have benefits.

With regards
John