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	$159.57	3.697%	$165.4693	$165.47	$165.45	$165.50
Purchase #2	$47.82	13.134%	$54.1007	$54.10	$54.10	$54.10
Purchase #3	$97.72	13.282%	$110.6992	$110.70	$110.70	$110.70
Purchase #4	$59.42	3.728%	$61.6352	$61.64	$61.65	$61.60
Purchase #5	$133.73	7.633%	$143.9376	$143.94	$143.95	$143.90
Purchase #6	$58.91	13.822%	$67.0525	$67.05	$67.05	$67.10
Purchase #7	$26.69	7.460%	$28.6811	$28.68	$28.70	$28.70
7 purchase totals =	$583.86		$631.5756	$631.58	$631.60	$631.60