Cover Letter should not come across as a heavy sales pitch of your background - don't oversell yourself. You want the hiring authority to know that you have interest in their position, BUT that there needs to be further exploration on the part of both parties. Your cover letter should include the following elements:
Educate the reader, from the perspective of what the job ad described, the potential match between your tax background and what they state they are looking for.
Reasons why you are interested in the position. These can include the type of tax work the position offers, or the location is one that you have been trying to get to because of family, children in school, etc.
Sum up by saying, "I look forward to further exploring whether this opportunity would be a good match from both our perspectives."
