title: Convert string into Currency format
body: <p>Using Ruby and Haml, I have a property which is cost. I believe (im new to ruby) that it will be a Float</p>
  
  <p>At the moment the below line outputs my decimal in format like 4.5 instead of 4.50, which is what I want.</p>
  
  <pre><code>%span.value= "&amp;pound;#{event.beers.first.cost)}"
  </code></pre>
  
  <p>This is my class file for beers.</p>
  
  <pre><code>class Beer
    include Mongoid::Document
    embeds_many :ratings
  
    field :name, type: String
    field :country, type: Country
    field :cost, type: Float
    field :photos, type: PhotoArray, default: PhotoArray.new
  end
  </code></pre>