twinned and shared Axis

Hello,
i have a small problem sharing axes with twinned subplots.

Here is a code snippet:

ax = fig.add_subplot(212, sharex = bx)
ax.plot()
grid()
cx = ax.twinx()
cx.plot()

The problem is, that both axis are independent. So on the left side, the tick
steps are 0.05 and on the right side 0.1.
The gridlines of the ax plot also do not match to the tickmarks on the right
side. How can i fix that?

Greeting

Matthias