First day of Diwali is known as Dhan Teras: This is the day of worshipping the goddess of wealth- Laxmi. The rituals and traditions are that you worship and pay homage to the symbols of wealth.
Many wash the coins with milk, water and honey to purify the wealth you receive through out the year. Some choose to put haldi kanku (turmeric and kumkum red powder) on bills and notes.