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	$55.28	4.204%	$57.604	$57.60	$57.60	$57.60
Purchase #2	$209.71	12.505%	$235.9342	$235.93	$235.95	$235.90
Purchase #3	$205.64	8.863%	$223.8659	$223.87	$223.85	$223.90
Purchase #4	$63.34	13.351%	$71.7965	$71.80	$71.80	$71.80
Purchase #5	$173.89	9.363%	$190.1713	$190.17	$190.15	$190.20
Purchase #6	$98.92	5.162%	$104.0263	$104.03	$104.05	$104.00
Purchase #7	$246.87	11.348%	$274.8848	$274.88	$274.90	$274.90
7 purchase totals =	$1,053.65		$1,158.2830	$1,158.28	$1,158.30	$1,158.30