Taiwan's currency is the New Taiwanese Dollar (NT$). Bills come in denominations of NT$100, NT$200, NT$500, NT$1000 and NT$2000. Coins come in units of NT$1, NT$5, NT$10, NT$20 (rare) and NT$50. Taiwan uses the local currency exclusively.
Tipping is not customary in restaurants or taxis (but is still appreciated). It is usual to tip the porter at better hotels (NT$100 is considered courteous). Many foreigners tip at better bars and clubs so staff may expect this. Note that the 10% service charge added to bills at many restaurants is not a tip to be shared with the staff.