Not too sure of what you want, but seems to be a mixed or left overs of differents method .
So if you want to text-align justify your links, drop all about floatting.
http://jsfiddle.net/69LjY/
some to read : http://www.barrelny.com/blog/text-align-justify-and-rwd/
/* NAVIGATION */
.navigation {
width:100%;
text-align:justify;
padding:0;
margin:0;
}
.navigation ul {
list-style-type: none;
margin:0;
padding:0;
line-height:0;
}
.navigation li {
font-family:Arial;
font-size:12px;
color:white;
background:black;
padding:5px;
margin:0px;
display:inline-block;
line-height:1.2em;
}
.navigation ul:after {content:'';padding-right:2700px;}/* line-height 0 + this avoid gaps under , padding , use widest screen width you like*/