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	$88.36	13.207%	$100.0297	$100.03	$100.05	$100.00
Purchase #2	$170.81	4.861%	$179.1131	$179.11	$179.10	$179.10
Purchase #3	$77.71	13.421%	$88.1395	$88.14	$88.15	$88.10
Purchase #4	$239.85	5.400%	$252.8019	$252.80	$252.80	$252.80
Purchase #5	$67.38	10.491%	$74.4488	$74.45	$74.45	$74.40
Purchase #6	$87.54	3.287%	$90.4174	$90.42	$90.40	$90.40
Purchase #7	$177.98	10.530%	$196.7213	$196.72	$196.70	$196.70
7 purchase totals =	$909.63		$981.6717	$981.67	$981.65	$981.50