If you haven't done so already, create a textbox on the main form where you want the totals to appear. In the control source for this text box, type in the following:
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=[Name of Subform].[Form]![Name of Field on Subform with Total]
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Replace [Name of Subform] with the actual name of your subform and replace [Name of Field on Subform with Total] with the actual name of the text box that holds the value on your subform.
I don't think you have to worry about the tabs as long as you reference the subform correctly. Just make sure the text box is on the tab you want it on.