[Mr. Bird]

In practice, would merchants list the pre-tax price, or would they advertise the gross price? Technically speaking, is it not ultimately the merchants' responsibility to pay the taxes? "Sales" tax vs. "purchasers" tax? So are we talking about an invisible (to the consumer) tax, similar to all of the currently embedded taxes and regulation on a product's price?

[kevkrom]

So are we talking about an invisible (to the consumer) tax, similar to all of the currently embedded taxes and regulation on a product's price?

Not really. I would expect that most retailers would list price including tax simply to avoid the "sticker shock" effect at the register, but nevertheless, the law requires the tax to be separately charged and stated on the receipt (exceptions for things like vending machines that are automated and don't provide receipts).

[Principled]

In practice, would merchants list the pre-tax price, or would they advertise the gross price?

I don't know. The prices of today include federal taxes but folks don't know it. The tax they usually don't include is state and local sales taxes. Who knows what merchants will choose to do.

Technically speaking, is it not ultimately the merchants' responsibility to pay the taxes?

Yes, consumers don't have to keep any records of purchases for any tax purposes. This makes the merchant liable for the tax. Of course, every receipt has a line item
"23% Federal sales tax $xx.xx"

So are we talking about an invisible (to the consumer) tax, similar to all of the currently embedded taxes and regulation on a product's price?

Every receipt must have a line item "23% Federal sales tax $xx.xx"

One of the big advantages, IMO, of this tax system is that we would all become more aware of the cost of government- leading to decreased spending.