How to cut power off when a certain voltage from a sensor is reached?
You don't want to use fixed voltage charge termination for NiCd batteries.  You do need to have some upper voltage limit as a safety, but charge termination is done with voltage slope and/or temperature.

NiCds exhibit a voltage "bump" when nearly fully charged with a reasonable current.  The voltage actually goes down just a little.  Therefore, look for the zero crossing of the voltage derivative, then add a little low current charge for a fixed time to top off the battery.  For example, here is a full discharge and charge cycle of a 3-cell NiCd battery pack:



The battery is discharged to effectively empty at 3.4 hours.  Until about 4.2h, a low charge current is used until the cells get to a sufficiently high voltage to be able to take "full" charge current.  Note how the voltage goes up, exhibits a bump, and then goes down again at about 6.4h.  The charge algorithm detects that by the zero crossing of the blue line and switches to low current top-off mode for a fixed 2 hours.

You are charging at a very low rate (.1C), so parts of this may not apply.  It would be a good idea to measure a charge curve to see where you are at.  Let it run long enough to know you fully charged the cell and see what both the voltage and derivative of the voltage look like.  At such a slow charge rate, a fixed ending voltage may be the only choice, but it would be good to see the data before deciding that.

The way to measure and detect this is in a microcontroller.  Each measurement will have some noise on it, but the signals are so slow that you can apply lots of low pass filtering.  The signals are so slow that meaningful filtering in analog will be difficult due to the very high impedances required to realize them, and the result error caused by leakage currents.  Digital values don't suffer from degradation over time, so you can do things like compute slope in volts/hour as I did for the blue line in the graph above.