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	$100.52	6.304%	$106.8568	$106.86	$106.85	$106.90
Purchase #2	$119.30	6.714%	$127.3098	$127.31	$127.30	$127.30
Purchase #3	$110.98	12.640%	$125.0079	$125.01	$125.00	$125.00
Purchase #4	$61.59	8.143%	$66.6053	$66.61	$66.60	$66.60
Purchase #5	$112.83	3.450%	$116.7226	$116.72	$116.70	$116.70
Purchase #6	$18.27	7.303%	$19.6043	$19.60	$19.60	$19.60
Purchase #7	$156.70	6.687%	$167.1785	$167.18	$167.20	$167.20
7 purchase totals =	$680.19		$729.2852	$729.29	$729.25	$729.30