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	$101.46	4.505%	$106.0308	$106.03	$106.05	$106.00
Purchase #2	$139.56	8.549%	$151.491	$151.49	$151.50	$151.50
Purchase #3	$16.91	7.326%	$18.1488	$18.15	$18.15	$18.10
Purchase #4	$9.91	4.771%	$10.3828	$10.38	$10.40	$10.40
Purchase #5	$103.50	10.408%	$114.2723	$114.27	$114.25	$114.30
Purchase #6	$44.54	4.730%	$46.6467	$46.65	$46.65	$46.60
Purchase #7	$145.82	8.791%	$158.639	$158.64	$158.65	$158.60
7 purchase totals =	$561.70		$605.6114	$605.61	$605.65	$605.50