Departure Tax - there is a slight sting in the tail as Roatan bids you 'see you soon' with a 38USD levvy and no its never included in your flight ticket. There are now some cases where it can be included so check your airline ticket and ask when you purchase. It still may be a point of arguing when you leave. Get a receipt if you do pay it and take it up with the airline.
Sales tax is 12% on goods purchased this is called ISV and is regular on most anything.
For tourism related goods like rooms and restaurant bills then this rises by a further 4% for Tourist Tax making 16% as you will see listed on most websites and your receipts.
