The official currency in the Tibet is the Chinese Yuan (CNY). The Yuan is also called Renminbi (RMB), or kwai. The Yuan notes are found in 100, 50, 20, 10, 5 denominations while the coins being 1, 0.5, 0.2, 0.1 denominations. It is better to carry some money in US dollar of all denominations.

Changing Currency:
The Only the central bank The Bank of China offers money exchange services in Lhasa of Tibet. The credit cards are accepted by only a few top hotels & shops in Lhasa. Therefore it’s advisable to carry local currency of all denominations while visiting Lhasa.

You may exchange the dollar or CNY into Nepali rupees at the Sino-Nepal Border but the exchange rate there may not be competitive. Many find it more convenient at Kathmandu money exchange centers.
The Banks in China/Lhasa are closed on Saturdays & Sundays.