I am thinking why not try this
you write a macro to copy paste deseired cells .suppose this mcro is called "test" then
right clilck the excel icon to the left of the <file> menu and vlick view code copy this event code.
Code:
Private Sub Workbook_BeforeClose(Cancel As Boolean)
If Day(Date)+1= 1 Then Application.Run test
End Sub
so on the last day of the month when you close the file the macro will be run. If you are thinking of last working day you have to modify the event code