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	$10.72	12.823%	$12.0946	$12.09	$12.10	$12.10
Purchase #2	$37.35	7.111%	$40.006	$40.01	$40.00	$40.00
Purchase #3	$57.26	9.363%	$62.6213	$62.62	$62.60	$62.60
Purchase #4	$53.36	12.708%	$60.141	$60.14	$60.15	$60.10
Purchase #5	$227.51	12.594%	$256.1626	$256.16	$256.15	$256.20
Purchase #6	$18.90	8.688%	$20.542	$20.54	$20.55	$20.50
Purchase #7	$249.77	11.710%	$279.0181	$279.02	$279.00	$279.00
7 purchase totals =	$654.87		$730.5856	$730.58	$730.55	$730.50