def five_minute_prices
      time = Time.zone.now.end_of_day
      first_price = Price.first.created_at
      prices = {}

      while first_price < time
        earlier_time = time - 300
        later_time = time
        prices[time] = []
        r = Range.new(earlier_time, later_time)
        Price.all.each do |price|
          prices[time] << price if r.cover?(price.created_at)
        end
        time -= 300
      end
      prices.reject { |key,value| value.empty? }
    end