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	$236.85	8.389%	$256.7193	$256.72	$256.70	$256.70
Purchase #2	$6.75	3.421%	$6.9809	$6.98	$7.00	$7.00
Purchase #3	$209.48	13.236%	$237.2068	$237.21	$237.20	$237.20
Purchase #4	$122.43	4.200%	$127.5721	$127.57	$127.55	$127.60
Purchase #5	$53.49	13.720%	$60.8288	$60.83	$60.85	$60.80
Purchase #6	$64.72	4.159%	$67.4117	$67.41	$67.40	$67.40
Purchase #7	$113.72	12.454%	$127.8827	$127.88	$127.90	$127.90
7 purchase totals =	$807.44		$884.6023	$884.60	$884.60	$884.60