The unit of currency in US is known as dollar. This currency has been adopted as the legal as well as official currency of various other countries. Congress of the Confederation of US has taken over the currency and this is the mostly used currency in all international transactions.
US also produce official coins starting from the year 1792. US dollar is unique and there has been various types of banknotes existing in the country. US dollar is based on the decimal system. This was created under the coinage act of 1792. There was not much dollar coins used in the country at that time.