When using single precision float, sin(x) and cos(x) (and possibly sincos and tan) are accurate for |x| < 128 (here, |x| means absolute value of x) but show increasing error as |x| grows beyond 128.

Here is a plot of the error of sin(x) as a function of x (compared to the single-precision float musl implementation of sin):

You can see that the error grows linearly beyond -128 / +128.

Looking at the code, there's a wrapper function that reduces the argument down to within +/- 128 and then calls the ROM code: https://github.com/raspberrypi/pico-sdk/blob/master/src/rp2_common/pico_float/float_aeabi.S#L637-L664 . That reduction is probably introducing a small floating point error for each loop of the reduction (that's a guess, I did not investigate further).

(Note: this was found running MicroPython's tests/float/cmath_fun.py test, which fails on a Pico board due to the above problem.)