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	$6.78	6.531%	$7.2228	$7.22	$7.20	$7.20
Purchase #2	$109.78	10.634%	$121.454	$121.45	$121.45	$121.50
Purchase #3	$61.45	13.773%	$69.9135	$69.91	$69.90	$69.90
Purchase #4	$193.28	6.131%	$205.13	$205.13	$205.15	$205.10
Purchase #5	$170.62	11.634%	$190.4699	$190.47	$190.45	$190.50
Purchase #6	$56.73	5.654%	$59.9375	$59.94	$59.95	$59.90
Purchase #7	$141.51	5.660%	$149.5195	$149.52	$149.50	$149.50
7 purchase totals =	$740.15		$803.6472	$803.64	$803.60	$803.60