You can set www or non www preference in nopcommerce by going to admin\Setting/GeneralCommon. Here
is the setting you need to change. If SSL is enabled in store setting it should redirect. If not all you need to add redirection manually in web.config.
I tried the setting that you suggested but it did not work. I already have the force SSL for all pages on.
Next I tried to use the web.config file to redirect to https. I found an example on the web but it broke the site. I've since removed it from the web.config and the site is still broken. I have my ISP looking into restoring it but is there an example of how to redirect to https that works for nopcommerce?