I've seen several references in the Eberron sourcebooks to paying taxes, but not any rates or tables for the actual amounts.
Am I overlooking something obvious?
Are they deeply hidden?
Or are they just non-existent?
At a guess, they're not meant to be mechanical in a hard-and-fast way. If you think it's appropriate for PCs to have to pay taxes, the books might have some suggestions as to who might be taxing them and why, but there probably aren't specific numbers for it.
This is all just conjecture on my part. I haven't read the parts in question, at least not in a long time.