Have two time values

1900-01-01 00:59:47.000 need to round up to
1900-01-01 01:00:00.000

1900-01-01 00:19:23.000 need to round down to
1900-01-01 00:19:00.000

Perferably using a function or something that does both on the same column!
Note the date above is the difference between as startdate and a enddate!

thanks
rag