For a lot of the time its quite common to be given say 5/5 on the METAR and it to be sever cavok or thick fog.
If you are working in F you have 1.8 covering 1 Deg Celsius.
so 5/5 Cavok would be 42/41 and thick fog would be 41/41 but it would still be record as 5/5 in Celsius.