We give our nanny a 5%-8% raise each year. We also added health insurance after the first year. She has been with us 5+ years.
For petty cash we used to do a cash reimbursement system (think big envelope, cash, receipts, itemized ledger), but it got to be a pain so we soon gave her a credit card and she submits all of the receipts. If she pays for anything in cash we reimburse her.