By 1820, the East India Company had established control over even those parts of India that it didn’t rule directly. But it quickly found that it was severely constrained by the diverse coinages in existence. It was spending too much on exchange.
This, by the way, is exactly what the Europeans were complaining of throughout the last quarter of the 20th century. That’s how and why the Euro was born.
In 1835 the Company Bahadur, like the EU would in 1994, decided to unify the currency system and introduced a new coin, the silver rupee. This was made the standard currency in Madras in 1818 and in Bombay in 1823. In 1835, via an Act, it became the standard currency throughout British India, replacing gold.