employee.rb

class Employee < ActiveRecord::Base
  ...

  def recent_tasks(options = {})
    completed_on = if options[:completed_on].present?
                     Date.parse options[:completed_on]
                   else
                     Date.current
                   end
    completed_on = 2.business_days.after(completed_on.to_time).to_date
    last_five_days = tasks.select('DISTINCT(completed_on)').where('completed_on <= ?', completed_on).order('completed_on DESC').limit(5).collect{|task| task.completed_on}
    tasks.where(:completed_on => last_five_days).order('completed_on DESC')
  end

  ...
end

task_controller.rb

class TasksController < ApplicationController
  respond_to :html,
    :only => :index
  respond_to :json

  ...

  def index
    @tasks = current_employee.recent_tasks params
    response.headers['Cache-Control'] = 'no-store'
    ...
    respond_with @tasks
  end
end