Queries :: Fill No Sales Months With 0

I am pulling sales results per customer and month. For presenting the numbers in a diagram I would like to show 0 sales for months in which no sales were generated. At the moment the query results only the months in which there are sales > 0. Is there a trick that I don't know?

SELECT Year([InvoiceDate]) & ' ' & Month([InvoiceDate]) AS [Month], totalsales_per_invoice([invoices]![InvoiceID],[invoices]![tax]) AS Ausdr1
FROM Invoices INNER JOIN customers ON Invoices.CustomerID = customers.CustomerID
WHERE (((Invoices.InvoiceDate) Between #1/1/2013# And #7/1/2013#) AND ((customers.CustomerID)=145))
GROUP BY totalsales_per_invoice([invoices]![InvoiceID],[invoices]![tax]), Year([InvoiceDate]), Month([InvoiceDate])
ORDER BY Year([InvoiceDate]) DESC , Month([InvoiceDate]) DESC;