If the conductor's adjusted ampacity were below the rating of the overcurrent device we are usually permitted to round up under most circumstances.
Where ever the code requires a conductor with a minimum ampacity, that is the ampacity after all adjustment and/or correction factors are applied. The rule in 240.4(B) does not change the ampacity of the conductor, it only permits you to use an OCPD that has higher rating than the conductor's ampacity.
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