It looks like all of the reasons I was going to give have already been said - to confuse people, make it more difficult to calculate odds, to bother people etc.
It does annoy me cause I like the round numbers but it virtually never changes my action. Fortunately players can not do that in live tournaments.
I HATE when they color out my greens ... takes away all my fun
I sometimes 3-bet people just because they bet weird amounts.
I see this every day now. People in MTT's seem to be raising instead of 1k chips its 999, or they raise like 327 just random as hell. I really dont get it.