In every state, including Florida, taxes on new vehicle purchases are mandated by the legislature. Where the dealer is charged with the tax collection responsibility at delivery, the dealer is regularly audited and held to a very high standard with loss of sales license as ultimate punishment. The dealer is highly unlikely in these circumstances to charge any non-legitimate taxes and these taxes are not negotiable.
A "Closing Fee" or "Documentary Fee" is not a legislated charge and is a dealer option. In many states this charge is limited in amount by law but is not regulated in Florida. I have seen dealer charges anywhere from zero up to $1595. This is a negotiable fee with the dealer and is simply additional profit to the dealer to offset clerical duties that have to be done.