Please descroibe what you want to see on your report.
This could be a list of all invoices for a given week or other date range with the individual totals, dates and customer names plus a grand total
This could also be a list of all items purchased with one row for each type of item with the subtotaled qty, dollars and so forth, also with a grand total.
The two options would usually be based on different layouts so it's important to spell out what you want.
Also, please list the tables/relationships involved. Do you have the typical data model for invoicing?