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	$63.42	12.675%	$71.4585	$71.46	$71.45	$71.50
Purchase #2	$174.62	8.636%	$189.7002	$189.70	$189.70	$189.70
Purchase #3	$112.29	10.855%	$124.4791	$124.48	$124.50	$124.50
Purchase #4	$173.30	10.455%	$191.4185	$191.42	$191.40	$191.40
Purchase #5	$236.87	9.421%	$259.1855	$259.19	$259.20	$259.20
Purchase #6	$111.91	13.536%	$127.0581	$127.06	$127.05	$127.10
Purchase #7	$105.65	5.777%	$111.7534	$111.75	$111.75	$111.80
7 purchase totals =	$978.06		$1,075.0533	$1,075.06	$1,075.05	$1,075.20