There's a very real, important reason why edits to questions and answers should generally be substantial. Every single edit to a post bumps it back up to the top of the "Active" page. So to prevent abuse, and to prevent the front page becoming littered with a series of older posts which have been only slightly edited, it's best to make edits substantial.
The other reason, a much less important reason, is that minor edits clog up the review queue.
So, keeping the above points in mind, edits to tag wikis have a much less effect on the front page than edits to questions and answers. When we edit tag wikis, there's less disruption to the actual Q&A. The review queue is seen only by users who choose to participate in reviews, whereas everyone, even visitors from Google, will see a cluttered front page.
Therefore, when I see tag wiki edits in the queue, as long as they're valid, I generally approve them. However, if I see a pattern of a user who spends time on just trivial edits in the tag wikis, to the point where it's bothersome, I might consider rejecting the edits, but it would take lots of these edits for me to do that.
Also, if it's clear someone is editing just for the +2 rep boost, I may reject the edit, but only if I'm absolutely certain. I prefer to err on the side of assuming people do what they do because they genuinely want to make the site better.
In general, it's best to make edits as substantial as possible. Why? Because someone may disagree with me and reject your edit anyway. So, don't just fix one typo; fix all the typos. But if there are no other problems that you see with the tag wiki, then fixing the occasional typo in a tag wiki shouldn't theoretically attract any negative attention. Just don't make it your life mission to go through all the tag wikis and make 2 character edits in one-sentence tag wikis. :)