You could use the CONVERT function for example:
DECLARE @Num4 AS DECIMAL(10,4)
DECLARE @Num2 AS DECIMAL(10,2)
SET @Num4 = 1234.9876
SET @Num2 = CONVERT(DECIMAL(10,2),@Num4)
SELECT @Num2
@Num2 will then equal 1234.99 -- note the rounding which has taken place.
of course this works as well
DECLARE @Num4 AS DECIMAL(10,4)
DECLARE @Num2 AS DECIMAL(10,2)
SET @Num4 = 1234.9876
SET @Num2 = @Num4
SELECT @Num2
@Num2 will then equal 1234.99 -- note the rounding