It looks like you already have it there, but I'm a bit confused by this line in your question: "Gross sales - Invoice amount".
If that is meant to be "Gross Sales = Invoice amount", then your formula would look something like:
"Your table"."Invoice amt"/SUM("Your table"."Invoice amt" by CASE WHEN "Inventory Organization"."Inventory Org Code" = 'KAD' THEN ' H & H' WHEN "Inventory Organization"."Inventory Org Code" in ('BAN','USA') THEN 'Bty' END,"Your table"."Fiscal Period").
It's easier to build these if you have separate columns for the components of a complicated formula. Then, you can assemble them using the "Column" selector in the formula editing window: