Twisting wires does cancel out the electromagnetic field. with regard to the illuminating light (assuming you have one) it is particularly important that the wires leading to the light are twisted.

What you should be concerned with is the electromagnetic field (which the twisted pair cancels out. Electromagnetism and magnetism are the same. This has nothing to do with RF radiation.

My suggestion is that you set the compass to go each of the four ways, and then turn on the switches, one by one, and see if any of them make any difference. If not, you are in good shape. If they all do, you are in terrible shape, and if only a couple do, you can do more to twist wires in the box, or alternatively, not turn on those switches.

Keep in mind that it is the flowing current that creates electromagnetic fields, not voltage. Also, the strength of the electromagnetic field is a function of the amount of current, and is not a function of the the voltage. No current flowing, no electromagnetic field.

Hope this helps.