How can I sum up the totals of groupings in views?

Question

I am trying to sum up my sales in my Commerce store by month.

I have created a view of completed payment transactions that is grouped by payment year (first grouping) and then payment month (second grouping). The config looks like this:

This gives output look like this:

Now what I'd like to do is sum up each month (the second grouping) to show the total sales for that month. I think I can use aggregation for this but I'm not sure how to set it up.

Answer 1

Most of the links I found for this kind of thing point towards Views Aggregator Plus. Apparently it allows you to "aggregate and group by column" (source).