This is specifically for NYC property tax. They have a paypal/venmo option on the payments screen, next to the options for echeck (no fee) and credit card (2% fee). I add a given gift card to my paypal account and then go through the property tax payment flow. Repeat until you're out of gift cards.

NYS estimated tax doesn't seem to have any limits on number of payments or cards so I didn't need to look for other options there. NYS has a slightly higher fee of 2.20% on credit cards, so again it depends on if that math works out for your needs and how much the card costs you.

IRS limits to 2 payments per quarter per SSN per payment site so splitting it up across gift cards doesn't work. The best I've found there is using a 2% card on sites that only charger 1.85-1.98% fees. Whether that is worth it depends on the size of your estimated tax bill and your credit limit. Eg in the best case that's 0.15%, or $1.50 "savings" on every $1k in tax payments. When you get to the number that's "worth it" you likely exceed your limit or don't care enough cause you're Daddy Warbucks rich.

All of these are probably pretty terrible ways to liquidate gift cards, but I'm not sure of a better one these days.