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	$58.65	12.651%	$66.0698	$66.07	$66.05	$66.10
Purchase #2	$42.84	13.849%	$48.7729	$48.77	$48.75	$48.80
Purchase #3	$90.63	5.457%	$95.5757	$95.58	$95.60	$95.60
Purchase #4	$42.44	9.731%	$46.5698	$46.57	$46.55	$46.60
Purchase #5	$90.67	5.107%	$95.3005	$95.30	$95.30	$95.30
Purchase #6	$50.26	8.350%	$54.4567	$54.46	$54.45	$54.50
Purchase #7	$91.27	13.306%	$103.4144	$103.41	$103.40	$103.40
7 purchase totals =	$466.76		$510.1598	$510.16	$510.10	$510.30