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	$152.47	11.803%	$170.466	$170.47	$170.45	$170.50
Purchase #2	$235.56	8.468%	$255.5072	$255.51	$255.50	$255.50
Purchase #3	$208.57	13.385%	$236.4871	$236.49	$236.50	$236.50
Purchase #4	$248.54	8.290%	$269.144	$269.14	$269.15	$269.10
Purchase #5	$137.45	9.556%	$150.5847	$150.58	$150.60	$150.60
Purchase #6	$35.35	13.201%	$40.0166	$40.02	$40.00	$40.00
Purchase #7	$177.58	7.357%	$190.6446	$190.64	$190.65	$190.60
7 purchase totals =	$1,195.52		$1,312.8502	$1,312.85	$1,312.85	$1,312.80