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	$10.77	13.240%	$12.1959	$12.20	$12.20	$12.20
Purchase #2	$53.95	10.631%	$59.6854	$59.69	$59.70	$59.70
Purchase #3	$187.98	13.859%	$214.0321	$214.03	$214.05	$214.00
Purchase #4	$11.95	7.553%	$12.8526	$12.85	$12.85	$12.90
Purchase #5	$37.49	8.436%	$40.6527	$40.65	$40.65	$40.70
Purchase #6	$115.85	13.214%	$131.1584	$131.16	$131.15	$131.20
Purchase #7	$71.35	13.389%	$80.9031	$80.90	$80.90	$80.90
7 purchase totals =	$489.34		$551.4802	$551.48	$551.50	$551.60