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	$12.60	7.319%	$13.5222	$13.52	$13.50	$13.50
Purchase #2	$80.53	8.693%	$87.5305	$87.53	$87.55	$87.50
Purchase #3	$169.56	4.705%	$177.5378	$177.54	$177.55	$177.50
Purchase #4	$155.78	5.554%	$164.432	$164.43	$164.45	$164.40
Purchase #5	$53.71	7.864%	$57.9338	$57.93	$57.95	$57.90
Purchase #6	$103.41	10.451%	$114.2174	$114.22	$114.20	$114.20
Purchase #7	$49.62	5.108%	$52.1546	$52.15	$52.15	$52.20
7 purchase totals =	$625.21		$667.3283	$667.32	$667.35	$667.20