For retail sales, the tax is 20.5%. Tax rates for on-premesis retailers is 13.7%. But yeah, for people just walking in and buying a bottle from the store, the tax is about a fifth the cost of a fifth. 
Huh. In all the states I’ve done some drinking in (especially CA, NV, FL), in 95% of bars if the menu says $5, you’re getting 5 ones back if you give them $10. And grocery/liquor stores charge usually regular sales tax. Any alcohol taxes are opaque and included in the sticker price. I expect weird alcohol laws in some states, but the PNW is not my first thought.