Sorting by the sum of a group from highest to lowest

I'm working on a project right now that has a list of customers and the sales generated. There are multiple locations for some, and others have just one location. I'm trying to sort the final sum of each customer from highest to lowest while keeping the grouping and have had no luck.

Here's an example of the spreadsheet:

Customer Total Sales

Customer1 800
Customer1 100
Customer1 200
1100 <---The sum is red text

Customer2 6500
6500

Customer3 500
Customer3 400
900

How would I be able to sort this so all the formatting looks the same but the sum is sorted highest to lowest so it would look like this:

Customer Total Sales

Customer2 6500
6500

Customer1 800
Customer1 100
Customer1 200
1100 <---The sum is red text

Customer3 500
Customer3 400
900

That could work. The Biggest problem is when customer1 is listed multiple times they aren't all the same, they all have a different city after them. Capture.PNG

Theres a picture of part of the sheet, theres more than 6000 rows so doing things manually would take up a lot of time. What I'm trying to do is keep everything grouped together but sorted by the red sum.