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	$7.65	11.455%	$8.5263	$8.53	$8.55	$8.50
Purchase #2	$49.45	10.258%	$54.5226	$54.52	$54.50	$54.50
Purchase #3	$175.85	11.438%	$195.9637	$195.96	$195.95	$196.00
Purchase #4	$11.42	8.205%	$12.357	$12.36	$12.35	$12.40
Purchase #5	$101.88	9.716%	$111.7787	$111.78	$111.80	$111.80
Purchase #6	$66.40	7.576%	$71.4305	$71.43	$71.45	$71.40
Purchase #7	$24.51	10.315%	$27.0382	$27.04	$27.05	$27.00
7 purchase totals =	$437.16		$481.6170	$481.62	$481.65	$481.60