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	$159.62	6.467%	$169.9426	$169.94	$169.95	$169.90
Purchase #2	$99.42	6.188%	$105.5721	$105.57	$105.55	$105.60
Purchase #3	$246.70	11.669%	$275.4874	$275.49	$275.50	$275.50
Purchase #4	$124.58	5.693%	$131.6723	$131.67	$131.65	$131.70
Purchase #5	$114.30	9.311%	$124.9425	$124.94	$124.95	$124.90
Purchase #6	$191.97	13.261%	$217.4271	$217.43	$217.45	$217.40
Purchase #7	$167.75	4.467%	$175.2434	$175.24	$175.25	$175.20
7 purchase totals =	$1,104.34		$1,200.2874	$1,200.28	$1,200.30	$1,200.20