What you can do is use a calc field like:
IF FIRST()==0 THEN WINDOW_SUM(AVG(1),0,IIF(FIRST()==0,LAST(),0)) END
with its compute using set to Brand, and then from the right-click context menu on your bin calculation pill, un-check the Ignore in Table Calculations option. This will cause partitioning on this field for all table calculations on this sheet.
Also you can simplify your bin calculation to:
IF SUM([sales]) <= 100 THEN "<100k" ELSEIF SUM([sales])<=500 THEN "500k" ELSEIF SUM([sales])<=1000 THEN "1000k" ELSE "1000k +" END
less conditional tests will evaluate quicker, because for an IF/ELSEIF/ELSE statement, Tableau matches on the first True result.
attached is an example.
revenue_band_test_jm_edit.twbx 13.0 KB