Ahhh, memories of being a lobby banker, circa 2005/2006. We called it "Change is Good" and for each Db card transaction on a regular checking account, we rounded up to the nearest dollar and put the pennies in the customer's Savings account. As I remember, there was no extra or special forms for the customer, they just gave their consent (maybe on a form), and it was set up in the back office to count & move the pennies. Each day's pennies were accumulated to make just one daily deposit.
The biggest challenge was defining the end points: which checking products do you want to transfer from, and which savings products catch the 'Change.' Be ready to explain why someone can't catch those pennies in a Money Market a/c. And think about how you'll treat the situation where a fraudulent Db card transaction gets backed out after its pennies post to Savings.
Marketing thought it was a great idea, but it lasted about 16 to 24 months before it burned out and had to be cleaned up: all those connections had to be undone, and I can't remember exactly how we notified customers that the program/product was ending.
Opinions or attitudes are mine, not those of my employer.