Add an option to encourage the bins to line up on integers, powers of tens, or (less frequently) small powers or two/five times those. There's a tradeoff between getting the right number of bins and minimize the power of two/five.
Possible multiples of powers of 10:
0: 1
1: 2, 5
2: 2.5, 4
3: 1.25, 8
4: 1.6, 6.25
5: 3.125, 3.2
We then choose the step size that minimizes the sum of
alpha times the number of steps, plus
the square of the log of the ratio between the requested number of bins and the number of bins using that ratio
Not sure of the proper value of alpha yet, that will take experimentation, and maybe it will be adjustable. Likely the default will prevent anything past 1 or 2, and if adjustable it will probably be capped at 5.