It depends if you want a still or sparkling cider. If still (i.e. non-carbonated,) you can use a non-fermentabele sweetener (Splenda or Stevia.) after all fermentaion is complete. I know some folks use Campden tablets to kill the yeast, and others just refrigerate. If you want sparkling (carbonated,) sweeten to taste with a non-fermentable, but you'll need to bottle with enough fermentable sugar to carbonate (without creating bottle bombs.) The forums have some good techniques to use. When I bottled, I always used a couple of 16 Oz soda bottles as a gauge. I tested every few days, and when they got rock hard, I'd open one to check carbonation. If it was to my liking, I'd pasteurize the rest. Again, there are some good techniques outlined, but be careful as putting pressurized glass bottles in hot liquids can be dangerous if not done properly.