This is a mac user protection issue. In some cases, keychain access is required to install software, you grant access if you know that you are installing software; you would deny if they warning popped up out of the blue. Another reason that the Mac might ask you to approve keychain access is that, by default, Turbotax wants to password-protect your tax return for privacy, and if the file password is stored in the keychain, you don't have to remember it.
