Department Sales Report (Tax Included in Sales)

I pulled a report called "Department Sales Report (Tax Included in Sales)". The overall total for "Sales" matches all other reports.

There is another column in the report called "Sales (Tax Ex)". This takes the sales figures (which does not include sales tax) and subtracts Sales Tax. I don't understand what this figure represents? What would this figure be used for? Why would anyone want to take sales and subtract sales tax? (I could understand sales PLUS sales tax to come up with the total amount tendered).

Any help would be appreciated.

Thanks!

Ken