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A 'coin of account' is a unit of money that does not exist as an actual coin (that is, a metal disk) but is used in figuring prices or other amounts of money. For example, the ''mill'' (or sometimes, ''mil'') is a coin of account in the United States. It is equal to one-tenth of a penny, and so to one-thousandth of a dollar (= $0.001), whence the name, which means "thousandth." There was never such a coin minted by the U.S. Federal government, though some states minted these coins well into the mid-1900s. Coins of account are used in accounting and for figuring taxes, usually either property taxes or sales taxes.