Is there a report that shows sales tax collected per invoice or per month? I didn't find anything.
Yes, if you go to Invoices (on the left hand navigation) you'll see a link on that page called 'Tax Report.' First filter the invoice list to what you need (i.e. between date ranges of a month) and then click the 'Tax Report' link and it'll use that filter for the report.
Got it, thank you Kevin!!