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	$11.31	11.392%	$12.5984	$12.60	$12.60	$12.60
Purchase #2	$93.82	11.496%	$104.6055	$104.61	$104.60	$104.60
Purchase #3	$165.87	3.723%	$172.0453	$172.05	$172.05	$172.00
Purchase #4	$247.41	8.800%	$269.1821	$269.18	$269.20	$269.20
Purchase #5	$36.78	6.501%	$39.1711	$39.17	$39.15	$39.20
Purchase #6	$213.65	9.681%	$234.3335	$234.33	$234.35	$234.30
Purchase #7	$223.59	13.339%	$253.4147	$253.41	$253.40	$253.40
7 purchase totals =	$992.43		$1,085.3506	$1,085.35	$1,085.35	$1,085.30