I don't think "it's a rounding error" is enough analysis here. A couple of meters of sea level rise, a couple of degrees temperature rise; these could be termed rounding errors.
Not degrees, thousandths of a degree, so possibly something like a centimeter if sea level rise.
Considering nuclear and fossil fuels directly release stored energy and solar increase albido this isn’t a 1:1 increase in energy. Further the earth radiates more energy from hot places than cool, still you can approximate it as something like:
Black body radiation is temperature in kelvin to the 4th power. (285 * (170,017^0.25 / 170,000^0.25) - 285) is an increase of ~0.007 C / (whatever our current percentage of energy from fossil fuels, nuclear, or solar).
So if our energy consumption increases by 4% per year (current global average) for ~110 years, we'd need to capture / produce as much energy as the Sun hits us with. Crazy!
I don't know if this would be any extra heat, because the radioactive material would already be decaying anyway if it was left in its natural state. Maybe the same problem where radioactive material would be left mostly underground and insulated where its heat would leak slowly.
Then again, part of the Earth's core heat comes form radioactive decay. So in a way, geothermal is an indirect form of nuclear fission.
We could rebase all of civilization on geothermal and the extra heat in the atmosphere would be a rounding error to the sun's energy.