#navigation_bar {
            overflow: hidden;
            list-style-type: none;
            width: 100%;
        }
            #navigation_bar li {
                text-align: center;
                float: left;
                width: 33%;
                border-style: solid;
                border-width: 1px;
                border-color: black;
            }

<ul id="navigation_bar">
    <li>Projection</li>
    <li>Real-Time</li>
    <li>Cleanup</li>
</ul>

<ul id="navigation_bar">
        <li class="first">Projection</li>
        <li>Real-Time</li>
        <li>Cleanup</li>
    </ul>
    ​

#navigation_bar {
                overflow: hidden;
                list-style-type: none;
                width: 100%;
            }
                #navigation_bar li {
                    text-align: center;
                    float: left;
                    width: 32%;
                    border-style: solid;
                    border-width: 1px;
                    border-color: black;
                    border-left:none;
}
#navigation_bar li.first {
    border-left:solid 1px black;
}

#navigation_bar li {
    border: 1px solid black;
    border-left-width: 0;
}

#navigation_bar li:first-child {
    border-left-width: 1px;
}

margin-right: -1px;

#navigation_bar {
        overflow: hidden;
        list-style-type: none;
        width: 100%;
    }
    #navigation_bar li {
        text-align: center;
        display: inline-block;
        width: 30%; /* Slightly smaller width to fix the borders */
        border-style: solid;
        border-width: 1px;
        border-color: black;
    }