Understanding Fees | Buying USDT with USD

I bought USDT with USD that I had in my wallet.
I guess it is considered a wallet method, is it? I spent $1350 while eventually getting just $1342.64
Please see a screenshot of the transaction. What are the $6.75 fee for? Is it a fixed amount or percentage of the USD amount ?. If I deduct $6.75 from $1350 I should get $1343.50 even. What is the additional difference of $0.61? Is it due to the exchange rate not being exactly 1/1 ($1/1 USDT)?

https://preview.redd.it/zgqehmnx4yt71.png?612&format=png&auto=webp&s=99d1a05b37cb5f5a953e5f64a7f73571c78148f3