Well this could be looked at as the same as the argument where low prices might be looked at as cheap quality. Yes, teens/tweens are on a low budget, and they will probably go for the cheaper item, but I think that you should want customers that buy your things because they really like it, not because it was cheaper than something else!
I was selling my jewelry really cheap and I would get a lot of sales, but the effort wasn't worth how much I was selling for (was making about $2-3 an hour). Well I upped my prices and someone actually bought a bracelet that I set for $18! It felt good to know that price wasn't a problem for them, and they paid for it because they really liked it (I hope!). :)
I also considered doing the .99 ending but I decided not to. I think it does give off a sort of grocery store/factory feeling, though.