Best way to exchange leftover Rupiah when leaving Bali?

By cutting out the middleman, QRIS (Gopay) should offer a more favorable exchange rate for IDR to supported currencies like SGD. This is because it facilitates a direct IDR -> SGD conversion, bypassing the need for USD as an intermediary currency. Using a money exchanger, on the other hand, may result in a worse rate due to the additional spread or fee incurred from converting IDR to USD and then to SGD. To verify this, you can try using QRIS and compare the rate with what a money exchanger offers.

I keep some cash at home for my driver to collect when I need a ride next time.

I gave the taxi driver on my last night in Lembongan around 230,000 rupiah. He was overjoyed, and I wished I had more to give.