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.
Well that is just wrong. Even if the 'residue' satoshi are in the wallet, you can't do anything about it. That's just forced unused amount. And it's not a small amount either. In this example if the person has 0.00078 bitcoins left in his wallet, that amounts to Rs. 580. You can't just force him to not use his Rs. 580 and keep it in the wallet because your website only allows 3 decimals instead of the full 8.