def build
      super do |builder|
        @zip_codes.each_with_index do |zip, i|
          builder.tag!('ZipCode', :ID => i) do
            builder.tag!('Zip5', zip)
          end
        end
      end
    end
def build
      super do |builder|
        @zip_codes.each_with_index do |zip, i|
          builder.tag!('ZipCode', :ID => i) do
            builder.tag!('Zip5', zip)
          end
        end
      end
    end
Given a list of zip codes, looks up what city and state they are associated with.

 The USPS api is only capable of handling at most 5 zip codes per request.