Determining the VA needed for a transformer, when I know the power DC
A good reference is this Hammond guide. 

If you are using full wave rectification from a single secondary, you will need a transformer of 5/0.62 * 36 = 290VA. If you are using a large filter capacitor to minimize the ripple, I would go a bit higher to be safe, maybe 350-400VA. 

In a full-wave rectifier-capacitor situation the current from the transformer is drawn in brief sharp pulses at the peak of each half cycle of the mains. The current is mostly limited by the dv/dt of the secondary voltage into the filter capacitor and by the resistance of the secondary winding plus the  dynamic resistance of the rectifiers. Since the peaks are relatively high, the RMS current is quite a bit higher than the average.  

Heating of the transformer windings is related to the RMS current, not the average.