CREATE DEFINER = 'my'@'%' FUNCTION `bank_round`(
        `x` DECIMAL(20,5),
        `d` INTEGER(1)
    )
    RETURNS DECIMAL(20,4)
    NOT DETERMINISTIC
    CONTAINS SQL
    SQL SECURITY DEFINER
    COMMENT ''
BEGIN
    DECLARE i INTEGER(1);
	
    SET x = x * POWER(10, d);
      
    IF ROUND(x)-x = 0.5 THEN 
        IF MOD(ROUND(x), 2) = 0 THEN 
   	    SET x = ROUND(x);
        ELSE
            SET x = TRUNCATE(x, 0);
       	END IF;
    ELSE 
    	SET x = ROUND(x);
    END IF;
    
    SET x = x / POWER(10, d);
    
    RETURN x;
END;

NOT DETERMINISTIC