Other than traders tokens, the only coins minted in 1858 would have been gold sovereigns or half sovereigns. They all have Queen Victoria on the obverse with the date under the queen and, "SYDNEY MINT", "Australia" and the denomination on the reverse. Any of these coins would be quite valuable. Apart from the previous, there was no Australian currency prior to 1911. What you probably have is a traders token. There were several Halfpenny tokens minted in 1858 for various traders. You may have something of value, if you can identify the token properly.
Token coins have an inscription on them, usually the business name and perhaps the address of the business, along with the value of the token.
Please provide this information for an estimate of value.
With the possible exception of traders tokens (with the traders business name on them), there were no "Australian" pennies minted prior to 1911.
The first Australian Dollar coin was issued in 1984.
Such a coin does not exist. The Australian Two Dollar coin was first issued in 1988.
Such a coin does not exist. The first Australian 10 cent coin was issued in 1966.
Such a coin does not exist. The Australian One Dollar coin was first issued in 1984.
The first Australian Two Dollar coin was issued in 1988.
The first Australian "Baby" coin sets were produced in 1993.
Such a coin does not exist. The Royal Australian Mint has never produced a Two Pence coin.
Such a coin does not exist. The Australian 2 cent coin was first issued in February 1966.
Such a coin does not exist. The Australian 1 cent coin was first issued in 1966. The Australian One Penny coin was issued from 1911 to 1964 inclusive.
Such a coin does not exist. The Australian 2 cent coin was first issued in 1966 on the introduction of decimal currency.
There is no Australian 1954 20 cent coin. Decimal currency was introduced in 1966.
There is no Australian 1950 20 cent coin. Decimal currency was introduced in 1966.