well sure you are going to see some jaggered edges of the circle... but they will be at the 1:1 pixel level. Typically a visitor does not zoom in that far.
You might try matching ground/ floor surface color around the circles edge using a Gif mat color... if your background is brown.. then use a brown mat around the object edge where it touches the background. For example, our 360texas.com logo below is sitting on a white mat matching a white background. General appearance is that is a nicely formed circle.. no jaggies.
Sometimes I put in a drop shadow... gives the appearance that the circle is floating about the ground/ floor.
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EasyPano - Panoweaver