I have nexus turned on in Florida, and my item is taxable however I am returning a 0 dollar rate for tax.
There are certain addresses in Miami that are designated by the Florida Department of Revenue as a tax free shipping address. There is a unique zip code assigned only to this address and it should not have any tax charged. The reason is that this business is engaged only in exports that are not subject to Florida sales and use tax.
https://pointmatch.state.fl.us/Default.aspx will allow you to search and confirm.