this was for the best western plus suites at tucson airport.. I was just price comparing after a Priceline win and was surprised to see that. I had never noticed it before and have used booking many times as sometimes they have deals the hotel website does not offer publicly.

I'm going to see playing around with hotels/dates if I see it on other dates/hotels/areas.

Here's another one at Tucson airport.. country inns and suites and even has an additional tax

Total price US$ 55.20
(for all guests)
TAX (12.05%) not included
Service charge (US$ 2) not included
City tax (6%) not included

It seems this may be a Tucson airport area fee as I have not found it at PHX nor in the city.

Then that will be a local tax and they may not be included in the price.
Booking does state that.

FYI They cannot be included because of the way the website charges it's clients, The hotels.

no.. not a tax. there are two taxes listed for some.. local and another PLUS this $2 service fee for tucson airport hotels.