About USD and SGD
US Dollar (USD)
The US dollar is divided into 100 cents and is used in the United States and several other economies, and many tourist businesses elsewhere quote prices in dollars. When a card terminal in another country offers to charge you in dollars, that is usually a dynamic currency conversion with a poor rate; choose the local currency instead.
Singapore Dollar (SGD)
The Singapore dollar is divided into 100 cents and is managed against a basket of currencies. Brunei dollars are accepted at par in Singapore. Hawker centres are often cash or QR-payment places, while larger shops take cards.
Exchanging USD for SGD
The rate above is the mid-market rate for USD to SGD. Banks, card networks and exchange desks usually apply a margin or a fee, so compare the amount you would actually receive. If a terminal offers to charge you in USD instead of SGD, decline: that conversion normally uses a worse rate.