越南某银行汇率http://www.vietinbank.vn/web/home/en/index.html
银联汇率http://en.unionpay.com/front_ExchangeRate.html
V家汇率http://usa.visa.com/personal/card-benefits/travel/exchange-rate-calculator.jsp
M家汇率https://www.mastercard.com/global/currencyconversion/index.html