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	$56.80	3.601%	$58.8454	$58.85	$58.85	$58.80
Purchase #2	$27.34	8.510%	$29.6666	$29.67	$29.65	$29.70
Purchase #3	$93.35	7.590%	$100.4353	$100.44	$100.45	$100.40
Purchase #4	$134.64	3.789%	$139.7415	$139.74	$139.75	$139.70
Purchase #5	$42.85	13.129%	$48.4758	$48.48	$48.50	$48.50
Purchase #6	$105.51	5.207%	$111.0039	$111.00	$111.00	$111.00
Purchase #7	$104.58	7.562%	$112.4883	$112.49	$112.50	$112.50
7 purchase totals =	$565.07		$600.6568	$600.67	$600.70	$600.60