Reported by forum user lawrenceyy in https://forums.adafruit.com/viewtopic.php?f=60&t=151793:

round(<integer>, <n>) throws NotImplementedError. User found this via round(0, 2). round(<float>, 2) is OK, as is round(<integer>).

This was working in 3.1.2, but broke as early as 4.0.0-beta.2. MicroPython 1.9.4 seems OK.