Voici un script SQL qui permet d'arrondir une date au quart d'heure le plus proche

DECLARE @MADATE AS DATETIME

SET @MADATE = '01/01/2011 10:07:29'

SELECT cast(round((cast(@MADATE as float(53))*24*4),0)/(24*4) as smalldatetime)

Résultat : 2011-01-01 10:00:00

SET @MADATE = '01/01/2011 10:07:30'

SELECT cast(round((cast(@MADATE as float(53))*24*4),0)/(24*4) as smalldatetime)

Résultat : 2011-01-01 10:15:00

Pour arrondir systématiquement au quart d'heure inférieur on utilisera la fonction FLOOR à la place de ROUND

DECLARE @MADATE AS DATETIME SET @MADATE = '01/01/2011 10:07:29'

SELECT cast(floor(cast(@MADATE as float(53))*24*4)/(24*4) as smalldatetime)

Résultat : 2011-01-01 10:00:00

SET @MADATE = '01/01/2011 10:14:30'

SELECT cast(floor(cast(@MADATE as float(53))*24*4)/(24*4) as smalldatetime)

Résultat : 2011-01-01 10:00:00