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	$53.49	13.521%	$60.7224	$60.72	$60.70	$60.70
Purchase #2	$54.94	7.433%	$59.0237	$59.02	$59.00	$59.00
Purchase #3	$18.35	11.796%	$20.5146	$20.51	$20.50	$20.50
Purchase #4	$71.28	11.682%	$79.6069	$79.61	$79.60	$79.60
Purchase #5	$195.30	10.693%	$216.1834	$216.18	$216.20	$216.20
Purchase #6	$7.50	9.728%	$8.2296	$8.23	$8.25	$8.20
Purchase #7	$206.53	11.665%	$230.6217	$230.62	$230.60	$230.60
7 purchase totals =	$607.39		$674.9023	$674.89	$674.85	$674.80