In a past life and the good old days of Sales tax I was selling packaging materials and food containers to restaurants and take away food outlets.
The sales tax, like today's GST , had to be shown separately on the sales docket. Unlike GST it was calculated on the cost price of the article ie our buying price. On a typical order there would be no tax on some items (white paper for wrapping fish and chips), 5% on some items (plastic takeaway containers) and 15% on some items (hot chip cups).
On writing a sales docket (yep writing) one had to have the selling price, the cost price and the tax rate for each product. Just to make life interesting, the sales tax on milkshake containers was 15% on 60% of the wholesale cost.
Why?? Because chocolate was exempt and someone had decreed that 40% of all milkshakes made were chocolate.
Keep up The Spirit