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	$250.89	6.430%	$267.0222	$267.02	$267.00	$267.00
Purchase #2	$10.43	3.780%	$10.8243	$10.82	$10.80	$10.80
Purchase #3	$72.65	11.313%	$80.8689	$80.87	$80.85	$80.90
Purchase #4	$206.72	8.187%	$223.6442	$223.64	$223.65	$223.60
Purchase #5	$10.49	5.833%	$11.1019	$11.10	$11.10	$11.10
Purchase #6	$66.35	9.420%	$72.6002	$72.60	$72.60	$72.60
Purchase #7	$140.35	11.484%	$156.4678	$156.47	$156.45	$156.50
7 purchase totals =	$757.88		$822.5295	$822.52	$822.45	$822.50