sql group by datetime on day

SELECT        DATEADD(dd, DATEDIFF(dd, 0, postDate), 0)
FROM          table
WHERE        (postDate >= @StartDate) AND (postDate < DATEADD(day, 1, @EndDate))
GROUP BY DATEADD(dd, DATEDIFF(dd, 0, postDate), 0)
ORDER BY DATEADD(dd, DATEDIFF(dd, 0, postDate), 0)