Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$77.65	6.471%	$82.6747	$82.67	$82.65	$82.70
Purchase #2	$151.53	4.648%	$158.5731	$158.57	$158.55	$158.60
Purchase #3	$100.34	4.806%	$105.1623	$105.16	$105.15	$105.20
Purchase #4	$10.43	3.290%	$10.7731	$10.77	$10.75	$10.80
Purchase #5	$101.58	8.266%	$109.9766	$109.98	$110.00	$110.00
Purchase #6	$31.73	13.317%	$35.9555	$35.96	$35.95	$36.00
Purchase #7	$37.29	11.733%	$41.6652	$41.67	$41.65	$41.70
7 purchase totals =	$510.55		$544.7805	$544.78	$544.70	$545.00