Looking into this a bit, I think the issue is that, really, we don't treat tabs special unless we're showing indentation changes. Instead, we leave it up to the browser. You can check this in your browser's developer tools, see if it's coming up as a tab or a series of spaces.
Given that, a combination of changing TAB_SIZE and setting the tab-size CSS property to what you want might be the way to go.
We can make a note to at the very least output a tab-size property based off TAB_SIZE, for future expansion options.
Christian