Upto what demical point coin works

suppose my fund unit is 5.218. can i redeem it completely in one go. Or i can redeem 5 unit only.

You can redeem units in multiples of 0.001. So yes you can redeem all of your 5.218 units at one go.

This is a screenshot of the MF redemption window where you can notice that Coin allows you to redeem all units or you can enter the units you wish to redeem in multiples of 0.001