This captures paths which are children of the top-level navigation elements, providing you place the routes in the :paths.

Tabbed navigation helper

def shopkeeper_navigation
  contents = ''
  links = [
    {:label => "Dashboard",                   :value => shopkeeper_dashboard_path,  :paths => []},
    {:label => "My Products & Services",  :value => shopkeeper_products_path,   :paths => [shopkeeper_services_path, shopkeeper_returns_path]}, 
    {:label => "My Customers",                :value => shopkeeper_customers_path,  :paths => [shopkeeper_promotions]},
    {:label => "My Shop",                     :value => shopkeeper_shop_path,       :paths => [shopkeeper_paypal_details_path]}, 
  ]
  links.each do |link|
    if (request.path =~ %r(#{link[:value]}.*)) || (link[:paths].any?{|path| request.path =~ %r(#{path}) })
      contents << content_tag(:li, link_to(link[:label], link[:value]), :class => "active")
    else
      contents << content_tag(:li, link_to(link[:label], link[:value]))
    end
  end
  contents
end