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	$208.91	6.368%	$222.2134	$222.21	$222.20	$222.20
Purchase #2	$76.50	9.840%	$84.0276	$84.03	$84.05	$84.00
Purchase #3	$11.77	4.268%	$12.2723	$12.27	$12.25	$12.30
Purchase #4	$94.52	5.160%	$99.3972	$99.40	$99.40	$99.40
Purchase #5	$32.94	4.844%	$34.5356	$34.54	$34.55	$34.50
Purchase #6	$12.53	3.315%	$12.9454	$12.95	$12.95	$12.90
Purchase #7	$81.55	10.622%	$90.2122	$90.21	$90.20	$90.20
7 purchase totals =	$518.72		$555.6037	$555.61	$555.60	$555.50