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	$99.63	11.554%	$111.1413	$111.14	$111.15	$111.10
Purchase #2	$212.34	5.557%	$224.1397	$224.14	$224.15	$224.10
Purchase #3	$183.45	11.369%	$204.3064	$204.31	$204.30	$204.30
Purchase #4	$51.74	4.290%	$53.9596	$53.96	$53.95	$54.00
Purchase #5	$110.63	8.204%	$119.7061	$119.71	$119.70	$119.70
Purchase #6	$77.70	10.479%	$85.8422	$85.84	$85.85	$85.80
Purchase #7	$116.76	13.455%	$132.4701	$132.47	$132.45	$132.50
7 purchase totals =	$852.25		$931.5654	$931.57	$931.55	$931.50