Code.Grandtotal() variable Resetting on new page in SSRS - ssrs-2008

Question

I have a complex expression that calculates the revenue depending on a bill type. It basically says if Bill type = Progress use X calculation , If Bill type = NTE use Y calculation , for everything else use Z. Because this is an Aggregate you can not sum up a total simply by using a sum function in SSRS. You need to use custom code. I have been using the following that I found on Stack. See below.
Public Shared Dim grandTotal as Decimal
Public Shared Dim costCenterTotal as Decimal
Public Shared Dim workerTotal as Decimal
Public Shared Function Initialize()
grandTotal = 0
costCenterTotal = 0
workerTotal = 0
End Function
Public Function AddTotal(ByVal b AS Decimal) AS Decimal
grandTotal = grandTotal + b
costCenterTotal = costCenterTotal + b
workerTotal = workerTotal + b
return b
End Function
Public Function GetWorkerTotal()
Dim ret as Decimal = workerTotal
workerTotal = 0
return ret
End Function
Public Function GetCostCenterTotal()
Dim ret as Decimal = costCenterTotal
costCenterTotal = 0
return ret
End Function
Public Function GetGrandTotal()
Dim ret as Decimal = grandTotal
grandTotal= 0
return ret
End Function
In my main expression I added the code.AddTotal() function to the expression and in the total line I used the code.GetGrandTotal() Function in the column.
The issue is that when I run the report I do not get the right total in the Grand Total Line . It seems to change depending on if I view each page of the report and even if I view all pages the Grand total is not correct. It seems to reset . Can some one tell me what I am doing wrong.
Thanks.