Quite right; my family has a few plastic "coins" that work just as well.
Here in the UK, shopping carts used to take a £1 coin, which incidentally had very similar geometry to the Indian 5 rupee coin (worth about 5 pence) - that was a great little find for our family, who always had a few 5 rupee coins lying around from our time visiting family in India. Sadly they updated the design of the £1 coin, so this trick no longer works.
Here in the UK, shopping carts used to take a £1 coin, which incidentally had very similar geometry to the Indian 5 rupee coin (worth about 5 pence) - that was a great little find for our family, who always had a few 5 rupee coins lying around from our time visiting family in India. Sadly they updated the design of the £1 coin, so this trick no longer works.