Personally, I think it's silly when people type non round numbers at all. Like a 299 bet instead of a 300. The only reason I can think of is to the graphic to look like more chips and possibly scare people?
I did see some people do this in small buyins and it was a flood. Back in the party poker
days. it was 3400 obviously cuz the guy's friend was sucking and the other was winning so he'd raise all but 1 chip and then fold to the 1 chip reraise. Haven't seen anything like that in years though and only saw it a couple of times then so no spreading rumors alright?
another reason is possible chats? I know pokerstars turns off the chat when someone is all in. If I'm having a good ol time chatting up with some other guy at the table and want to put someone all in and keep my chat, I'd think about this and try to get the chat for a few more minutes.
I think there has to be another reason than just a bet though.