neo is not divisible coin. So you have to buy, sell, send or receive it in integer form. Such as, 1,2,30,40 etc. You are not allowed to buy, sell, send or receive it in decimal form, so if you try to send it in decimal form, the transaction would be rounded up and you might lose 1 neo (1 neo is about $115 today). I don't know why, but the dev have designed neo in such way. Maybe for simplicity reasons or something like that.