There are two types of taxes you need to worry about with Bitcoin.
The first is regular income tax. If you earn bitcoins by mining or doing any other kind of work, you must declare the market value of your bitcoins as earned income whether you sell them or not.
So you are telling that if i draw a great painting, i must decrale its market value as earned income, whether i sell it or not?
actually, until you sell it it has no value. consider bitcoins under the capital gains rules and taxes due when it it converted to fiat. Technically, if you spend the Bitcoins you mined you would most likely be required to pay taxes on the fiat value of what you bought. as long as you keep your bitcoins bitcoins and don't spend them i doubt taxes would be required.