You are correct, the hotel tax is in fact 10%. Most places also charge 10% service charge so I believe you are seeing a typo. It should probably read "$104.00 plus 20 % tax & service". Notice the & is over the 7 on a normal keyboard...

In 2019, please keep Agape Cottages in mind in Cane Garden Bay. We are one of the few places that do not add a service charge. Of course, we are required to add the 10% government hotel tax.

Cheers,
Jason