If Fed is really using statistical techniques, then it is impossible to come at an answer in multiple of 25 points unless they are targeting an objective, else they are using guess work and using tradition as the excuse. OLD quarter point system, could benefit the ultra rich, they should use the decimal points increase similar to stock market.
Doctors prescribe antibiotics or other medicine by weight very precisely in developed countries like USA, but in developing countries a child is given half of the antibiotics( where the child may be even 1/5 th weight of adult dose or 3/4th. So in Medical science we progressed, but not in banking.
With that said, there is no real reason for this kind of policy/tradition or simplicity.
Interest rate has a ripple effect across the entire U.S. economy and economist use gear analogy ( also ) then in cars more transmission are better, same is true with interest rates.
Ask big corporation how even a single point change affect: $9 trillion corporate debt
Or ask a student how does a single point affect , students collectively has 1.5 Trillion in debt.
Or ask a saver/retiree, who is not getting a fair safe return. Balance is key and it comes with precision. more granular interest rate change can generate efficiency.