you ca get more familiar with cast ans convert
Date and time data from January 1, 1900, through June 6, 2079, with accuracy to the minute. smalldatetime values with 29.998 seconds or lower are rounded down to the nearest minute; values with 29.999 seconds or higher are rounded up to the nearest minute.
--returns time as 12:35
SELECT CAST('2000-05-08 12:35:29.998' AS smalldatetime)
--returns time as 12:36
SELECT CAST('2000-05-08 12:35:29.999' AS smalldatetime)