I'm not so sure.
From tags (emphasized by me)
A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.
If I would like to see how other people implemented the mergesort, then I would look at the merge-sort tag. There is a huge difference between a mergesort and a bubble-sort, with regards to skill-level required, speed, code structure, you name it! Now, in what way is merge-sort similar to bubble-sort? They both do the same thing in the end, sure, but there's a big difference in the way that they do it.
I would prefer having both algorithm-specific tags and a more general tag. The algorithm-specific tag wikis could specify that the "sorting" tag should preferably be used as well.
mergesort is a subset of sorting, just like python-2.7 is a subset of python. This doesn't mean that it all should be grouped together under one tag.