Examine The Datetime Values

Accuracy of Datetime in SQL Server is 0.00333 millisecond. The millisecond part of value will be converted to a closer times of 0.00333, which is also rounded up to the precision of 1/1000.

0.00333 * 2 = 0.00666
0.00333 * 3 = 0.00999

DECLARE @testDT DATETIME
SET@testDT ='2012-11-11 00:01:00.003'
--this returns  '2012-11-11 00:01:00.003'
SELECT @testDT
SET  @testDT ='2012-11-11 00:01:00.004'
--This returns  '2012-11-11 00:01:00.003'. Because 0.004 is closer to 0.00333 than 0.00666
SELECT @testDT
SET  @testDT ='2012-11-11 00:01:00.005'
-- --This returns  '2012-11-11 00:01:00.007'. Because 0.005 is closer to 0.00666 than 0.00333
--0.00666-0.005=0.00166; 0.005-0.00333= 0.00167
SELECT @testDT
SET  @testDT ='2012-11-11 00:01:00.006'
--SET  @testDT ='2012-11-11 00:01:00.007' 
--SET  @testDT ='2012-11-11 00:01:00.008'  
--above values will all be converted to 0.007 because they are closer to 0.00666 than 0.00999
SELECT @testDT
SET  @testDT ='2012-11-11 00:01:00.009' 
--This returns  '2012-11-11 00:01:00.010'
SELECT @testDT