不同的浏览器做出不同的决定，阅读这些链接了解更多信息：

> http://ejohn.org/blog/sub-pixel-problems-in-css/
> http://elasticss.com/determination-of-algorithms-used-for-percentage-based-rounding-divs-on-browsers-and-css-frameworks/

我特别喜欢John Resig / David Baron的这个解释，为什么这甚至是一个问题：

I was talking this over with some
Mozilla developers and David Baron
explained the situation quite well:

We’re trying to meet a bunch of
constraints that can’t all be
satisfied at the same time (the proof
is left as an exercise to the reader,
though I may have actually written it
out once in a Bugzilla comment):

1. 4 adjacent objects of width/height 25% (for example) starting at one edge
   of a container should end exactly at
   the other edge; there should never be
   an extra pixel in the container and
   they should never be wrapped due to
   being a pixel to wide

2. objects that are logically adjacent should always touch visually; there
   should never be a pixel gap or a pixel
   of overlap due to rounding error

3. objects given the same width should occupy the same number of pixels

4. object boundaries should always (visually) be aliased to a specific
   pixel boundary in the display (they
   should never be blurred)

The one [Mozilla] sacrifices is
typically (3),except for borders
where we sacrifice (1) by rounding the
widths to pixel boundaries much
earlier.

看到这个问题，一个强制一致的JavaScript修复：

Evenly distributed height of child elements with CSS

另一个相关问题：

Are the decimal places in a CSS width respected?