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	$226.99	12.528%	$255.4273	$255.43	$255.45	$255.40
Purchase #2	$169.40	13.122%	$191.6287	$191.63	$191.65	$191.60
Purchase #3	$99.90	5.583%	$105.4774	$105.48	$105.50	$105.50
Purchase #4	$115.35	10.179%	$127.0915	$127.09	$127.10	$127.10
Purchase #5	$210.79	8.581%	$228.8779	$228.88	$228.90	$228.90
Purchase #6	$59.41	12.144%	$66.6248	$66.62	$66.60	$66.60
Purchase #7	$245.28	12.472%	$275.8713	$275.87	$275.85	$275.90
7 purchase totals =	$1,127.12		$1,250.9989	$1,251.00	$1,251.05	$1,251.00