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	$84.51	9.434%	$92.4827	$92.48	$92.50	$92.50
Purchase #2	$126.63	11.278%	$140.9113	$140.91	$140.90	$140.90
Purchase #3	$94.52	11.336%	$105.2348	$105.23	$105.25	$105.20
Purchase #4	$60.73	9.673%	$66.6044	$66.60	$66.60	$66.60
Purchase #5	$177.96	4.359%	$185.7173	$185.72	$185.70	$185.70
Purchase #6	$48.40	4.763%	$50.7053	$50.71	$50.70	$50.70
Purchase #7	$25.71	5.164%	$27.0377	$27.04	$27.05	$27.00
7 purchase totals =	$618.46		$668.6935	$668.69	$668.70	$668.60