Cash use is in decline but a staunch advocate hit a wall when trying to work out how much it costs to produce coins.

A collection of rare Australian and international coins and banknotes worth $2.5 million is heading for auction next week.

Explore More: These 4 Rare Nickels From Over 20 Years Ago Are Worth a Ton Now For You: 5 ... Australian dollars and cents, similar to the U.S. system. The majority of Australia’s most valuable ...

It led to a surge in demand for the US dollar and, together with evidence of weaker Australian inflation, led to the local currency sliding to a five-year low of just under 61 US cents.