Following from the post below it seems that it is not so easy for Top 5 Customers.
As Customer is ENTITY how is it attached to Sales? There Account Transactions, Account Values, and Accounts and so on.
REQUEST: @emre would be a good feature to be able to supply a Max Results Parameter to all REPORT TAGS. Therefore I could use the standard {REPORT ORDER:x} Tag - using Sum and Desc key words PLUS maybe MAX keyword to return only 5 lines.
No need for SQL DETAILS just would return TOP n / BOTTOM n for any Report Tag!