Can you use a baud rate with zero error? Like 125K?
The processor leaves the factory with the internal oscillator calibrated to ±10%. It is possible to tune the oscillator to ±1%. In addition to dealing with the baud rate error you may have to tune the oscillator.
You could tune the oscillator to run a bit slow and get closer to 115200 baud rate. Unfortunately everything else (millis, delay) will also run a bit slow.