Assuming 75 degrees C, like most electrical wiring terminations and conductors are, the 10AWG is compliant. The breaker is not there to provide overcurrent protection, only ground fault and short circuit protection. The overcurrent protection is provided by the A/C unit. The wire should be sized to handle the minimum circuit amps, and the breaker sized to meet the max fuse to allow power spikes during start-up.
If you are using NM cable, however, you would be limited to the 60 degree C column per 334.80, so you would be .4 amps over the rating of the wire. (Of course I would still pass it... I don't think there is any scientific basis to limit NM cable to 60 degrees when it is also required to be listed at 90 degrees C per 334.112, and I hardly think .4 amps will cause a noticeable issue.)
