I have a cube of sales transaction measures (sales, qty) and time and
customer dimensions.

For a given set of time "t" I want to get a count of customers with
sum(sales) in "t" by total sales bucket, ie 10 customers with $0 to $100, 50
customers with $100 to $200, etc.

Where do I start with this query? I've been trying FILTER() but haven't made
much headway.