The Euro is widely accepted throughout Greece, and you'll use it for most transactions.
While major credit and debit cards are widely accepted in Sifnos, it's a good idea to carry some cash. When paying for services, such as taxis or in cafes, it's common to pay in cash. Credit cards are widely accepted in hotels, larger restaurants, and shops.
Tipping is a common practice in Greece. In restaurants, it's customary to leave a tip, typically rounding up the bill or leaving around 5-10% of the total. In cafes, rounding up is also common. Tipping is appreciated but not mandatory. In hotels, it's customary to tip hotel staff, such as the housekeeping and bell staff.
It's advisable to exchange currency at banks or authorized exchange offices for the best rates. Avoid exchanging money at airports or in tourist areas where rates may not be as favorable.
While traveler's checks were once widely used, their popularity has declined with the widespread acceptance of credit and debit cards. It's recommended to use cards and cash for most transactions.