Wat.rb

class Invoice
  
  %w(sender_details recipient_details).each do |method|
    define_method method do
      attributes[method]
    end
  end

  %w(total_amount tax_amount).each do |meth|
    define_method("#{meth}=") do |value|
      currency_config = Invoicing::CurrencyValue::CURRENCIES[currency] || Invoicing::CurrencyValue::CURRENCIES[area.currency]

      super(
        BigDecimal(value).round(
          currency_config[:digits],
          Money.rounding_mode
        )
      )
    end
  end
end