I think there is a nice trend online for services charged at a round rate, these aren't impulse purchases. But please post any results if you do an experiment!
I originally remembering hearing about this 'phenomenon' during undergrad. It's a common heuristic that we think the gap is much larger than $.01 when it comes to the $4.99 -> $5.00 jump.
On a semi-related note, I remember telling all my friends in the music biz how iTunes was making a huge mistake by crossing the $1 threshold when they jumped up from $.99 to $1.29 ... at <$1, fans didn't think too much about the purchase. once they crossed it, it only accelerated the progression of pirating.
Here's a link to the pretty extensive study that two guys from Cornell published -- Heuristics in numerical cognition: implications for pricing http://forum.johnson.cornell.edu/faculty/mthomas/HeuristicsI...
On a semi-related note, I remember telling all my friends in the music biz how iTunes was making a huge mistake by crossing the $1 threshold when they jumped up from $.99 to $1.29 ... at <$1, fans didn't think too much about the purchase. once they crossed it, it only accelerated the progression of pirating.