Honestly, I don't see the point on branding your website as a "Tether price calculator" unless you're expecting a de-peg. USDT > USD seems a bit redundant.
Latest reports and investigations showed that Tether is not really backed by US dollars and its value is not exactly the same as for dollar.
Which reports are you talking about? The last ones I saw said that they aren't totally backed by actual US dollars on a bank account, not that they aren't worth $1. If they are backed by other assets worth the total amount of USDT in circulation, then they are tecnically backed. Also, the market gives it a value of $1.