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	$50.81	11.634%	$56.7212	$56.72	$56.70	$56.70
Purchase #2	$72.58	10.222%	$79.9991	$80.00	$80.00	$80.00
Purchase #3	$111.67	11.644%	$124.6729	$124.67	$124.65	$124.70
Purchase #4	$121.70	8.842%	$132.4607	$132.46	$132.45	$132.50
Purchase #5	$35.44	5.872%	$37.521	$37.52	$37.50	$37.50
Purchase #6	$18.27	10.664%	$20.2183	$20.22	$20.20	$20.20
Purchase #7	$101.49	3.837%	$105.3842	$105.38	$105.40	$105.40
7 purchase totals =	$511.96		$556.9774	$556.97	$556.90	$557.00