Assume your data looks this:
Cust Amt
Smith 12
Jones 43
Taylor 48
Smith 8
Miller 24
Taylor 3
Miller 12
Create a Pivot Table
Layout: Row field = Cust, Data field = Sum of Amt
Options: Uncheck Grand totals, Autoformat
You should end up with this:

Cust Total
Jones 43
Miller 24
Smith 20
Taylor 51

Create 2 columns like this
Bins Hits
20 1
50 2
90 1

Select the numbers in the Pivot Table and name them ArrayP.
Name Bins.
Select the 3 cells under Hits and enter this array formula with
Ctrl+Shift+Enter:
=FREQUENCY(ArrayP,Bins)