Sales Top 5 Items In Current Context =
CALCULATE ( [Sales], TOPN ( 5, VALUES ( Sales[Item] ), [Sales] ) )
Sales Top 5 Items Regardless of Item Filter =
CALCULATE ( [Sales], TOPN ( 5, ALL ( Sales[Item] ), [Sales] ) )
Sales Top 5 Items Intersecting with Current Context =
CALCULATE (
[Sales],
TOPN ( 5, ALL ( Sales[Item] ), [Sales] ),
VALUES ( Sales[Item] )
)