Majority of the so called "luxury taxes" (that were really named so) existed maybe one or two hundred years ago, mainly targeted then-existing aristocracy, but most of such special taxes are long gone. (Maybe the after-effects are still showing up in weird places, like your clerk's imagination...) One gem was the literal "tax on fun" (which applied to cinema shows and dance halls), but that was discontinued in the 1950s. I guess only "luxury taxes" that we have now are quite "normal" by Western standards, like sales taxes on confectionery and alcohol and cars.

More recently, a couple of generations ago there might have been import tariffs on consumer electronics...?

I can't think any other tax on the product itself than the regular 24% value added tax. (Of course, the indirect ones, like income tax paid by employees, tax on corporate profit, etc probably show in the final price.)

Foodstuffs do have lower VAT rate (around 10%), so maybe the clerk was thinking about that, but that difference doesn't explain a 5€ -> 100€ hike. Maybe you just managed to wander to the most expensive retail store in the downtown and had an unusual camera model...

Finland is expensive place, but most of that caused by more mundane reasons than special "luxury tax", like indirect taxes, regulation, and shipping costs raising the general price levels.