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	$93.43	12.537%	$105.1433	$105.14	$105.15	$105.10
Purchase #2	$106.59	5.727%	$112.6944	$112.69	$112.70	$112.70
Purchase #3	$89.70	13.240%	$101.5763	$101.58	$101.60	$101.60
Purchase #4	$220.60	12.479%	$248.1287	$248.13	$248.15	$248.10
Purchase #5	$6.53	13.367%	$7.4029	$7.40	$7.40	$7.40
Purchase #6	$17.66	4.577%	$18.4683	$18.47	$18.45	$18.50
Purchase #7	$46.64	3.240%	$48.1511	$48.15	$48.15	$48.20
7 purchase totals =	$581.15		$641.5650	$641.56	$641.60	$641.60