I am not an expert, but in my opinion, people usually do/submit their taxes, so the keyword "taxes" has more value than the root word "tax" in this case. Coupled with a non-.com domain, I think the resale value is low.
My advice is to be very selective about the domains you register. There are many junk domains with low resale value that even I fall "victim" into buying, getting an underpriced, decent domain (not even say a ultra-good one) is hard and takes patience.
I know this is a domain forum but I find this modified quote from Warren Buffett (veteran stock investor) to be suitable for domaining: "[The domain aftermarket] is a place where money from impatient people gets transferred to patient ones."