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	$152.46	11.679%	$170.2658	$170.27	$170.25	$170.30
Purchase #2	$208.64	7.795%	$224.9035	$224.90	$224.90	$224.90
Purchase #3	$11.73	8.313%	$12.7051	$12.71	$12.70	$12.70
Purchase #4	$194.89	13.685%	$221.5607	$221.56	$221.55	$221.60
Purchase #5	$165.61	7.690%	$178.3454	$178.35	$178.35	$178.30
Purchase #6	$90.52	9.833%	$99.4208	$99.42	$99.40	$99.40
Purchase #7	$220.65	11.275%	$245.5283	$245.53	$245.55	$245.50
7 purchase totals =	$1,044.50		$1,152.7296	$1,152.74	$1,152.70	$1,152.70