In sports they tend to add half a point to prevent ties from occurring, for example:

Here is a point spread line from a NCAA Men's Basketball game tonight. In a point spread, you take the team's *actual* score and subtract whatever number the bookie sets for the point spread, in this case 3.5 points. In order for money on Temple to win they would need to win their game tonight by 4 or more points to cover the spread - winning by 3 points exactly will mean that Temple "loses" by half of a point in the eyes of a bookie.
They do the same things for over/unders as well. An over/under bet in sports, which is referenced so frequently here, is a bet on the total number of points scored in a game by both teams. For example, in a basketball game hey will set a line at like 131.5 points so there will be a clear cut winner and no opportunity for a push.