I have not used Pixastic before. But, I believe, every time the image is clicked, you should increase the angle of 90.
First Click -> 90 Second Click->180 Third Click ->270 Fourth Click ->360 Fifth Click ->90..etc
Updated:
It seems Pixastic first deletes the image and inserts it again. This is why the onClick handler runs once. Change it to live and it will work.
$('#tok').live('click',function() { $(this).pixastic("rotate", {angle:90}); });
Check out the Demo: here.
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