Thanks Itooh!
Regarding the rounding of frequencies or tuning to a scale, you currently can recreate something like that by outputting MIDI and synthetizing those MIDI into a DAW or instrument, and muting the this tab. But it's not a contained solution.
I have to say though, I quite like when you both hear the tuned notes from the MIDI output and the real frequencies from tonejs' PluckSynth I'm using.
Maybe I will add the a "tune-to-midi-notes" option after all :) Thanks for the suggestion!