Pivot table row total INCORRECT

I am exporting data from Access into Excel and then creating a pivot table to summarize. For some reason 6 of the 6336 summarized rows has an invlaid amount in the Grand Total cell for the row ( like 4.44089209850063E-16 when it should be 0).
I tried converting the amounts to currency on the Access side before exporting to Excel, but the six continued with non-zero amount in total cell.
I also searched Microsoft Excel to see if there was a 'fix' for this - but, no joy, possibly because I don't know the correct terms to search under.
I even tried exporting and creating the pivot table manually (normally everything is done via a module in the Access database). But even manualy, those 6 rows are wrong.
This problem is ruining my results. Solutions? Thoughts?