Try this:
SELECT EmpID, FirstName, LastName, Address, Salary
FROM (
SELECT EmpID, FirstName, LastName, Address, SUM(Salary)as Salary
FROM Employee
GROUP BY EmpID, FirstName, LastName, Address
UNION ALL
SELECT NULL AS EmpID, NULL AS FirstName, NULL AS LastName, 'Total Salary:' AS Address, SUM(Salary)as Salary
FROM Employee
GROUP BY EmpID, FirstName, LastName, Address
) AS T