I thought that had more to do with the fractured taxing powers of the Feds, state and various local taxing authorities. For example Florida sales tax is 6%, but my county charges a 1% tax to provide sand road maintenance and paving. Pretacking is easy enough once in the stores, but somewhat odd when dealing with taxed and no taxes items.

It's the same in Canada: different sales tax/VAT rates in different provinces on different goods. E.g. HST on clothes in Ontario but no tax at all on clothes in P.E.I. I think it does have a lot to do with the federal system. The UK is unitary, so there is a flat 20% VAT on everything taxable, which is included in the sticker price. I wonder if Australia includes tax?

The UK has three different VAT bands: 20%, 5%, and 0%. (And then there's VAT exempt items, which aren't the same as 0%!)

See, e.g., https://en.wikipedia.org/wiki/Value-added_tax_(United_Kingdo....

The Australian GST is national and included in the display price of all good sold.

(There are some goods - eg Fresh Fruit and Vegetables - that are exempt from it -- but if GST is applicable - then it is included in the displayed price)