To be safe, I like to just bottle the cider normally, and then add Splenda at drinking time. Two reasons for this.
1) You can give the cider to others with varying sweet-tooths, and everyone'll be happy. (This is a big one for me - I make my cider in huge batches with my roommates, and we all have very different sweetness preferences!)
2) You mess up and add too much, you've totaled 12 oz of cider - not 5 gallons.
3) Cider is some unpredictable stuff. It can taste completely different from one week to the next at the beginning of its aging, and from one month to the next later on. What seems like it needs sweetening now may not at all in a few months time - and you'll feel real silly if a perfectly-aged cider has become perfectly-aged alcoholic soda pop because you added Splenda to the level that tasted right when you were bottling, and sampled your fermentey, yeasty, green brew!