smalldatetime

smalldatetime defines a date that is combined with a time of day. The time is based on a 24-hour day, with seconds always zero (:00) and without fractional seconds.

If the seconds are 29.998 or less it rounds down to the nearest minute. If the seconds are 29.999 or more rounds up to the next minute.

http://msdn.microsoft.com/en-us/library/ms182418.aspx