Animating rotations using jQuery
Instead of that complex switch statement, I'd just use an option object:

var allLinks = $('nav ul li a');
var rotation = 0;

$('nav').on('click', 'ul li a', function() {
    'use strict';
    var $this = $(this);
    var item = $this.parent();
    var navAll = $this.parents('ul');

    var option = {
        '0_1': {
            rotateAll: '-=90deg',
            rotateThis: '90deg',
            rotation: 270
        },
        '0_2': {
            rotateAll: '-=180deg',
            rotateThis: '180deg',
            rotation: 180
        }
        // Add them all here
    }[ rotation + '_' + item.index() ];

    if ( option ) {
        navAll.transition({rotate: option.rotateAll});
        allLinks.transition({rotate: option.rotateThis});
        rotation = option.rotation;
    }
}


There are 2 more things to consider:


Are you sure you really need that nav ul li a selector? Wouldn't nav a do the job just the same? While we're at it, why are you listening to the click on the a elements, and then find the li via .parent()? Can't you just listen to the click event on the lis themselves?
Is there any method to that configuration? I wasn't able to deduce any algorithm from what you've provided, but I'm sure there is. You'd be better off calculating it on the fly, if possible.