T-SQL Functions can also be created using the CREATE FUNCTION syntax.

CREATE FUNCTION [MyRound]
(
    @Operand Decimal,
    @Places Int
)
RETURNS DECIMAL
AS
BEGIN
    DECLARE @x decimal;
    DECLARE @i int;
    set @x = @Operand * power(10,@Places);
    set @i = @x;
    set @x = @i + iif((@x - @i) >= .5,1,0);
    set @x = @x / power(10,@Places);
    RETURN(@x);
END

This creates a function that implements a custom round based upon the POWER and the places argument.

SELECT MYROUND( 2.569, 2 ); -- 2.57 
SELECT MYROUND( 2.5649, 2 ); -- 2.56

You can then use it in your own application using the above syntax.

Functions in Data Builder

The user defined functions show up in Data Builder under the programmability area.