Each domain's value would depend on the rarity and whether or not end users exist for the domain.
I don't see the value being too high due to the limited uses in the Bitcoin Taxes niche. The main buyers would be Tax consultants, advisors, and/or blogs related to Bitcoin Taxes. Even then, the domain would need to be desirable (i.e. short, descriptive, brandable, etc.)
Your best bet is listing the domains for sale in the Digital Goods marketplace subforum and waiting for an interested buyer.
You can use
http://namebio.com to search sales history of domains with various options like keyword, age, price, etc.