Coinsecures website doesn't let you enter a Bitcoin amount with more than 3 digits after the decimal point. So if you made a purchase of 0.055 Bitcoins you will get 0.05478000 Bitcoins because they charge 0.4% fee, which is totally fine. They even show how much you get in their wallet.

Now here's the problem if after some time you want to sell off those Bitcoins and you try to enter 0.05478 guess what? YOU CAN'T.
All you can do is enter 0.054 and CONGRATULATIONS you just lost 0.00078 Bitcoins.