We have a B6432 site asking this and I've looked a little in the source code and can't answer it. For them, for October, they had one cancelled order for 4,500 (they show their currency as points instead of dollars). Their monthly sales and sales over time match, but annual sales is 4,500 more for October.
September is really weird- they have one cancelled order for 1,125 but the discrepancy is 4000.
I checked a 9.0.4 site and they are showing a similar discrepancy for October-annual sales includes cancelled orders.
Shouldn't all three totals for October match.
See attached document. SalesDiscrepancy.doc (340kb) downloaded 5 time(s).

Well, I guess I can't subtract, I just took her word for the 4500. I just checked a third site and they are seeing discrepancies also.

Thanks. If you come up with fix please post it.
Also, when looking at date discrepancies and trying to tie them to specific orders, I noticed that on 9.0.4 and previous sites, on the manage orders screen, if you want to include orders for the last day of the month, you have to select the first day of the next month as the end date. For example, October 31 orders didn't show until I set Nov 1 as the end date.