Need to insert nested totals for text boxes in SSRS List Tablix cell

Question

This article is SOOOOO close: How to create a report with sections and page breaks using SSRS, at this link: How to create a report with sections and page breaks using SSRS. Using a UNION between the tables we can get the vertical hierarchy we want, using the List Tablix. Using a LEFT JOIN between the tables, we can use a regular tablix to get the totals we want but we get all counties first, then all townships rather than as shown, County with its monthly breakdown followed by its townships with their monthly breakdown.

IF we can insert a total, somehow, some way ... it'll work OR if we can get the List Tablix functionality in a full blown Tablix, that should do it.

Need to get totals on these text boxes:

Here is where I need the totals:

Answer 1

Of course the answer was simple -- another developer and I looked at this and he tried another approach -- adding a row and then adding a total. Something like it was tried before but the total arrived at was for every payment.

What can I say? Overthinking is a disease ... find an intervention group! :)