I've seen a few people do it, seems to be a bunch of reasons behind it. Some are OCD, some do it when they've got a certain kind of hand. And I think some do it to disguise the kind of bet they're making - notice that Tom Dwan does it a lot playing live. Where others will bet $15,000 he'll bet $15,700 or $14,900 or something.
I don't bet odd numbers, but I tend not to bet in exact multiples of the big blind either because it can make it really obvious what you're doing. I've seen players who'll make a raise preflop from late position and from the amount you know they're following the "Raise 3BB plus 1BB for each limper"
rule, which tells
you something about their play. If you deviate from the exact amounts a little bit, your opponents don't get that extra information. Assuming they're paying attention in the first place.