Waldo is correct. It is verutally impossible to stop an active fermentation. You need to get the wine down to under 40 degrees for several days to stop the fermentation or add a lot of sulfites, which might kill the taste of your wine.
The better approach is to ferment the wine to dryness. Then add back sugar to sweeten to tatse. This is the most reliable method to make sure you get the correct alcohol level, correct sweetness and don't end up with exploding bottles. I have an article on this method at:How to Sweeten Your Wine