By simply rounding up to the nearest whole number maybe? We're essentially talking about that theory that you could keep dividing by half and either add it ant never reach 1 or subtract it and never reach zero.
There's a point at which the numbers are so infinitesimally small it isn't even negligible anymore to count, it just might as well be nothing in a practical sense relative to the scale you started. +1/2, +1/4, +1/8, +1/16, +1/32, +1/64... Percents of percents, I mean, we're splitting hairs here and doing all this math...for what? You could keep scaling down in theory but if every point up or down is half the distance of the last, from last, that it was to the prior, its insignificance to the original scale grows accordingly.
Since it's practically nothing after a certain point you might as well say the addition/subtraction or just movement, has simply stopped. You could add another '9' to .99999999...... Most folks (and almost all calculators) would just simply round it out.