Earlier quoted context omitted.
I have a feeling that's optional. It may even be regional. My experience was almost exclusively Tokyo. I traveled to Tokyo for over 20 years, and always paid what was on the sticker. I was told that the tax was included in the price. I remember one of my bigger purchases, was a ¥75,000 Oceanus watch, and that was exactly what I paid.
If you go to a donqi the price tags list without the tax besides small text that either lists the full price or says "+10% consumption tax" or along those lines. As a tourist you don't always have to pay the consumption tax though.
I remember the saleswoman asking to see my passport, when I was buying the watch (it was that big department store in Akihabara).