I don't use cash much, but I do write checks and use my debit card often. I "Save the Change" by rounding up to the nearest dollar. I've managed to save $100 in one month that way.
So in my ledger if I wrote a check or used my debit card for $52.40, I'd make a note in one column for the exact amount spent and then in the balance column, I write in $53 and deduct that. That way I can verify incase there are transfer errors and then figure my savings balance.