I cannot find a TA agreement with NCL, but here is one from Carnival. I am sure that NCL's agreement read pretty close.
"Travel Agency agrees and acknowledges that it is an agent of its respective customers. Travel Agency is not an agent of Carnival
, other than as may be applicable with respect to certain General Sales Agents in non-U.S. jurisdictions, in which case the underlying Travel Agency Agreement will specifically set forth such agency relationship. Nothing in this Policy shall be deemed to give Travel Agent the right, license, authorization or approval to make bookings with Carnival or to receive any commission or any other payments directly or indirectly from Carnival, as the terms of any such payment or commission must be set forth in an underlying Travel Agency Agreement between Carnival and Travel Agent. It is understood that individual consumers booking Carnival cruises for themselves and/or for others and who are not receiving any commission or payments from Carnival are not ‚ÄúTravel Agents‚Ä? hereunder."
(I insert the BOLD
That said, the NCL passenger contract does say that NCL can raise the price basically for any reason. If you don't like it, you can cancel.
So I guess that the tax part of this moot.
Spending too much time on this since the OP paid the tax and is not going to chase the rest of the money. Let's move on.