Just as a heads up: I have just submitted the first version of NYC Sales Tax Calculator for iOS to Apple. Unlike the Android version which exists in free and paid flavors, the iPhone release is always free, but displays banner ads. The app is compatible with all iPhones (but not iPads) running iOS 8 or better. It should be available within the next 8 days, give or take.
A version for Windows Phone 8 is also planned, but unfortunately my newly purchased Lumia 630 died instantly after using it the first time, so it went straight back to Amazon for “repairs” (they’ll very likely just trash it and send me a new one).