Make your own RANK calcs.
RANK( AVG([Sales]), 'desc')
Then filter for [that calc] <= 10.
If you want to see top-10 AND bottom 10 at the same time, do:
If [that calc] <= 10 or [that calc] > window_MAX([that calc])-10 then 1 else 0 END
Put that on the filter shelf and select for value = 1.
Ah yes, of course. Thank you so much Joe!