How can I use my customer's checkout form to track my inventory?

Ok, so right now I have 3 forms.  Each customer, upon completing their shopping, checks out using one of the forms.

How can I use the information automatically generated by my jot forms to create an accounting spreadsheet for myself where I would see totals of each style/size sold, total sales, totals for taxes, totals spent on shipping?

It looks like all the 3 forms are having same fields. You may consolidate the form submissions by exporting them to an excel report. 

https://www.jotform.com/help/44-How-to-Export-Form-Data-to-Excel

Once you have all the 3 submission reports, you may merge them to one file by copy & pasting the rows. 

Not sure if it helps, but you may also take a look at JotPayments App that might help you in viewing a report of the payments received.

http://apps.jotform.com/app/jotpayments

Hope this information helps! If you are referring to something different or need any further assistance, please let us know.  We will be happy to help!