are you looking to get a grand total of all of the "TotalItemValue" numbers?
if so, try this:
SELECT [Item Number], Dimensions, Zero, One, Two, Three, Four, TotalItemValue, SUM(TotalItemValue) AS GrandTotal FROM (
SELECT [Mock Value].[Item Number], [Mock Value].Dimensions, [Mock Value].Zero, [Mock Value].One, [Mock Value].Two, [Mock Value].Three, [Mock Value].Four, Sum([Zero]+[One]+[Two]+[Three]+[Four]) AS TotalItemValue
FROM [Mock Value]
GROUP BY [Mock Value].[Item Number], [Mock Value].Dimensions, [Mock Value].Zero, [Mock Value].One, [Mock Value].Two, [Mock Value].Three, [Mock Value].Four
)
GROUP BY
[Item Number], Dimensions, Zero, One, Two, Three, Four, TotalItemValue