default_tax.rb with different calculation method

default_tax.rb

def compute_order(order)
  matched_line_items = order.line_items.select do |line_item|
    line_item.product.tax_category == rate.tax_category
  end

  line_items_total = matched_line_items.sum(&:total)
  round_to_two_places(line_items_total - ( line_items_total / (1 + rate.amount) ) )
end

def compute_line_item(line_item)
  if line_item.product.tax_category == rate.tax_category
    round_to_two_places(line_item.total - ( line_item.total / (1 + rate.amount) ) )
  else
    0
  end
end