What audit do you mean? Is there an institution that deserves to audit tether.to? I don't know if any institution has the right to audit a crypto project. By the way, if even a project is audited, I am not sure the team will publish the detail to the public. You must contact the team if you are really curious about the audit. For me, as long as it is one of the top crypto coins, it will be quite safe although no audit announcement on the site.