Fix large number rounding

These two instances of rounding down result in errors at certain large numbers where one would expect the next unit to begin.

``` js
formatNumber(1e23);
// => '99,999Q' (expected '100s')

formatNumber(1e26);
// => '100,000s' (expected '100S')

formatNumber(1e29);
// => '100,000S' (expected '100O')

formatNumber(1e35);
// => '99d' (expected '100d')

formatNumber(1e38);
// => '99D' (expected '100D')

formatNumber(1e59);
// => '99^' (expected '100^')

formatNumber(1e62);
// => '99,999^' (expected '100*')
```