When trading stocks is it a first in first out as far as taxes are concerned?

Sorry in advance for not having the right verbiage but

Lets say a year ago you bought 100 shares of a company

and last month you bought another 10

as far as taxes are concerned, if you sell 50 shares now are you selling 50 of the original 100 shares you bought so you would pay the lower tax rate on the profit

or does the gov look at it like you bought 10 a month ago so you pay the higher tax rate on just the profit from the 10 and then pay the lower on the other 40 shares?

or do they charge you the higher amount on all of it?

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Hope this makes sense and thanks for your answers!