You ever wander into a store and wonder why merchandise is priced the way it is? Why this item is $X.99 and the item right next to it is $X.97? Wisebread published a great article on the psychology of pricing back in April. I believe there are applications for this information in the context of selling on Etsy.
For me, I can't ever see myself pricing a hand-made craft at $9.99 when I could just round up to $10. This comes from my experience selling at fairs and conventions. I am not walking around with coins in the cashbox and handing back pennies if I can avoid it. But it might be worth looking into if you want to pull in a certain kind of online audience.
It's almost like you have to play a game with pricing until you get it just right.