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	$160.28	6.333%	$170.4305	$170.43	$170.45	$170.40
Purchase #2	$240.95	7.369%	$258.7056	$258.71	$258.70	$258.70
Purchase #3	$32.45	9.403%	$35.5013	$35.50	$35.50	$35.50
Purchase #4	$239.55	5.718%	$253.2475	$253.25	$253.25	$253.20
Purchase #5	$7.75	10.335%	$8.551	$8.55	$8.55	$8.60
Purchase #6	$66.65	9.305%	$72.8518	$72.85	$72.85	$72.90
Purchase #7	$190.83	7.146%	$204.4667	$204.47	$204.45	$204.50
7 purchase totals =	$938.46		$1,003.7544	$1,003.76	$1,003.75	$1,003.80