The math is a bit counter intuitive, but increasing by 5% then decreasing by 5% of the new value does not get you back to the start exactly.

You take a value v, increase it by 5% to 105% of the previous you now have 105% * v. Now you take that new values as the basis for the next calculation, and decrease by 5% to 95% of the previous, you now have 95% * 105% * v which is actually 99.75% * v.

You need to find the day from which their wealth increased by 5.263% so that a 5% tax would bring them back.

But yeah, whatever it doesn’t make a material difference to the argument. A one time tax sounds a bit weird to me, but I don’t live there, Californians should do whatever they can. Maybe a one time tax is a good first domino stone.