As it's been said already, here on Tapastic, not quite yet. The tagging system has unfortunately not been integrated much (as of yet) so there isn't a huge difference in whether you tag or not at the moment.
In the future though, or for other websites like Tumblr, Wordpress builds, etc.? Then yes, tag that shit. That's SEO optimization right there, and whether or not you tag your work with "webcomic" could mean the difference between an entire Twitter comic community discovering your comic and, well, not discovering it lol