Dr.Monzer Kahf, a prominent economist and counsellor states: “Interest earned from a conventional non-islamic bank is not the owners’ from the Shari’ah point of view. The account holder does not own it. It is still owned by the bank but since it is given by the bank according to its own system and within the law one does not return it to the bank but MUST GIVE IT TO MUSLIM CHARITY. The moment you got it, it becomes due to charity and you never own it.
On the other hand, interest you owe the income tax authority is imposed on you unjustly (or may be justly because you must not delay payment of your legal obligations) but it is imposed on you as a person. This makes it your duty to pay it and you cannot use money that you do not own for this purpose. In my opinion you made a wrong judgment by delaying tax payment and you know it is going to create interest payment. You should not let it do that by paying it on time.”