Align twinx tick marks

Is it possible to make a plot with two independent y-axes such that the tick marks align?

Below is an example of half of the solution. I've doubled the y-axis using twinx, but the tick marks aren't aligned and the gridlines form an awkward pattern on the plot. Is there a way to make the tick marks share the same positions, but correspond to different y-values? In the example below, I would like the tick mark for 5 on the left to be at the same vertical position as the tick mark for 6 on the right.

import numpy as np

a = np.random.normal(10, 3, size=20)
b = np.random.normal(20, 5, size=40)

fig, ax1 = plt.subplots()
ax2 = ax1.twinx()
ax1.hist(a)
ax2.hist(b)

The overarching point of this exercise is to make the grid lines overlap for the two axes.

You need to manually set the yticks as it stands these are automatically calculated resulting in a variation. Adding something like this:

ax1.set_yticks(np.linspace(ax1.get_ybound()[0], ax1.get_ybound()[1], 5))
ax2.set_yticks(np.linspace(ax2.get_ybound()[0], ax2.get_ybound()[1], 5))

where we set the ytick locations using an array of 5 points between the bounds of the axis. Since you have a histogram you could just set the lower value to zero in each case, and you may want to have the upper bound somewhat larger, so I would instead have

ax1.set_yticks(np.linspace(0, ax1.get_ybound()[1]+1, 5))
ax2.set_yticks(np.linspace(0, ax2.get_ybound()[1]+1, 5))

Giving a plot (with a change of color and transparency (alpha) for clarity):