One old trick for making tabs without border bottoms on the active tab, and also without involving tables, is to make your tabs as a series of inline elements inside a container, then to follow them with a gap element which is wider than the container, filled with non-breaking spaces.
If the gap element and the last tab are clear:none, and the container is overflow:hidden, then the wide element should be cut off at the edge, providing a visually filled edge border ignorant of the widths of the tabs. Unfortunately, WebKit ignores the clear:none, and wraps the long gap element, creating a very broken appearance. All other major browsers (ff, ie, opera, icab) get this right.
Example code with screenshots of correct and incorrect rendering can be found here: