Calculation Showing Inaccurate Answer I can not get this calculation to display the answer I need. I am sure it is my lack of SQL Server skills, but this is my conundrum.

In the sample DDL Below, I am wanting to run the query (1111-666)/1111 which broken down is 450/1111 which equates to .4050

When I run each calculation step individually (AnnualSales, DeptSales, Tax) the SUM() is accurate, but when I try to run one equation to get me the ONE result that I need, I keep getting .7889 as my answer.

What in this query should be changed so that my output is .4050?

Declare @Calc Table
(
  employee varchar(100)
  ,annualsales decimal(10,2)
  ,dep1sales decimal(10,2)
  ,dep2sales decimal(10,2)
  ,dep3sales decimal(10,2)
  ,dep4sales decimal(10,2)
  ,dep5sales decimal(10,2)
  ,tax decimal(10,2)
)


Insert Into @Calc (employee, annualsales, dep1sales, dep2sales, dep3sales, dep4sales, dep5sales, tax) Values
('emp1', '1111.00', '26.12', '83.00', '16.55', '21.77', '87.08', NULL)
,('emp1', NULL, '28.07', '11.00', '101.24', '47.03', '76.19', NULL)
,('emp1', NULL, '35.25', '7.00', '33.64', '43.54', '43.52', NULL)


Select 
employee
,SUM(ISNULL(annualsales,0)) AnnualSales
,SUM(ISNULL(dep1sales,0)+ISNULL(dep2sales,0)+ISNULL(dep3sales,0)+ISNULL(dep4sales,0)+ISNULL(dep5sales,0)) DeptSales
,SUM(ISNULL(tax,0)) Tax
,SUM((
    (ISNULL(annualsales,0))
    -    (ISNULL(dep1sales,0)+ISNULL(dep2sales,0)+ISNULL(dep3sales,0)+ISNULL(dep4sales,0)    +ISNULL(dep5sales,0))
    +(CAST((ISNULL(tax,0)) AS INT)))
    /NULLIF(ISNULL(annualsales,0),0))
FROM @Calc
GROUP BY employee
ORDER BY employee asc
You should get the correct result if you perform your calculation using the sums for each part instead of performing the calculation on each row and summing the result. 

rextester: http://rextester.com/ZGQ51639

Declare @Calc Table
(
  employee varchar(100)
  ,annualsales decimal(10,2)
  ,dep1sales decimal(10,2)
  ,dep2sales decimal(10,2)
  ,dep3sales decimal(10,2)
  ,dep4sales decimal(10,2)
  ,dep5sales decimal(10,2)
  ,tax decimal(10,2)
)


Insert Into @Calc (employee, annualsales, dep1sales, dep2sales, dep3sales, dep4sales, dep5sales, tax) Values
('emp1', '1111.00', '26.12', '83.00', '16.55', '21.77', '87.08', null)
,('emp1', null, '28.07', '11.00', '101.24', '47.03', '76.19', null)
,('emp1', null, '35.25', '7.00', '33.64', '43.54', '43.52', null)
,('emp2', 1954.85, '1120.65', '0', '0', '0', '0', 392.70)


Select 
employee
,AnnualSales=sum(isnull(annualsales,0)) 
,DeptSales  =sum(isnull(dep1sales,0)+isnull(dep2sales,0)+isnull(dep3sales,0)+isnull(dep4sales,0)+isnull(dep5sales,0)) 
,Tax        =sum(isnull(tax,0)) 
,[SomeCalc] =(sum(isnull(annualsales,0))
             -(
               sum(isnull(dep1sales,0)+isnull(dep2sales,0)+isnull(dep3sales,0)+isnull(dep4sales,0)+isnull(dep5sales,0)) 
             +(sum(isnull(tax,0))*.75)
              )
             )
            /nullif(sum(isnull(annualsales,0)),0)
from @Calc
group by employee
order by employee asc