@Mark42 Unfortunately Airbnb doesn't collect sales tax (also referred to as Occupancy Tax) in all areas which makes it a pain for those of us that have to collect and pay individually. I'm also in the same situation as you. Here's what Airbnb has to say:
https://www.airbnb.com/help/article/654/what-is-occupancy-tax--do-i-need-to-collect-or-pay-it
As you can see there are two options, neither are very satisfactory. Should you decide to collect from the guest you can send a Special Offer for each reservation increasing the price for the tax or collect when the guest arrives. I find this awkward and combersome so I just include it in my nightly price. But that has downsides too: my price is then higher than it should be and I wind up paying the 3% Airbnb on the money that I ultimately send to my county.
Hopefully, as time goes on, Airbnb will program a special feature for adding the tax and relieve us of this burden. But until then....