[edit] and playing around with the increment of x it keeps throwing in some magical values which are a repeating pattern in hex, with the LSB off by one usually...
0.CCCCCCCC.... = 4/5 had anything to do with it.
Using hexadecimal we have
5 * 3 = 10 - 1, so
5 * C = 40 - 4 so
5 * (1 + C + C0 + C00 + C000...) = 5 - 4 + 40 - 40 + 400... where the last term is = 0 mod 2^32
-----
D
0.CCCCCC.... = 4 / 5
So why would it take its digit from 4 / 5 and not 1 / 5? Because it takes x=4 to make the 5-x subtraction in 5 - x + x0 - x0 + x00 to come out to 1.
So this gives us a general rule for inversion (for numbers less than 16). Take the hexadecimal expansion of (n-1) / n, truncate to get enough hex chars, add 1 to the least significant hex digit.
I.e. the inversion of 3 would be 0xAAAAAAAB