Yes, it is very important to say where you are, because no two countries/states have the same tax laws 100%. There's always something different between them. 
For example, in the USA on the federal tax return you would have to report the mined bitcoin as of the day you received it as income. So if it was $450 when you received it, you report $450 income and pay regular income tax on that amount. Then if you sell it at $490, since you already paid taxes on the $450 you don't pay taxes on that part but pay cap gains taxes on the profit of $40.
For example, in the USA on the federal tax return you would have to report the mined bitcoin as of the day you received it as income. So if it was $450 when you received it, you report $450 income and pay regular income tax on that amount. Then if you sell it at $490, since you already paid taxes on the $450 you don't pay taxes on that part but pay cap gains taxes on the profit of $40.