The only way I have found to hide transactions in Mint so they can't be seen is to use a browser extension called ad-block plus with the chrome web browser. Just go to the chrome web store and search for adblock. It's free by the way, but it is most certainly worthy of a donation.
For me I had to restart chrome for it to fully function. After restarting go to Mint, right click on the transaction you want to hide, highlight adblock and select block this ad.
Now a pop up window should appear,
Just slide it until it is gone click it looks good then it will go to another pop up screen and there you can confirm it and you are done.
