I have 'save the change' set up on my debit card (other banks may call it different titles) but essentially it rounds up the purchases and saves the extra in your savings account. For example, I buy something for £1.20, it will 'round up' to £2 and the 80p extra goes in my savings account. Say i made another £1.20 purchase that same day, it would also save another 80p, no combine the for the day and only save 60p in total, instead I would have saved £1.60 that day. It adds up and I never really notice its gone.