If you set a analog clock or watch to that time, both hour and minute "arms" point diagonal upwards, which (with some imagination) look like the "mouth" of a smiley > which is "happy". So it's supposed to give the 'buyer' a 'happy feeling' and is supposed to "persuade" them buy a clock / watch.
At least.. that's what I've been told.
btw.. i have the same thing with xx:45.. had it 3 times this evening :s
I am the same but I think it's simply because I can usually geuss the time within a minute or 2 of accuracy (and i'd imagine most people can) when i'm at School, and so you tend to "check the time" at certain times
To me this is one of those theories that is just a coincidence, sorta like how more awkard silences happen within 5 minutes of 20 minutes to the hour or 20 minutes from the hour.