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	$233.83	8.855%	$254.5356	$254.54	$254.55	$254.50
Purchase #2	$139.67	12.569%	$157.2251	$157.23	$157.25	$157.20
Purchase #3	$234.83	3.223%	$242.3986	$242.40	$242.40	$242.40
Purchase #4	$143.88	4.857%	$150.8683	$150.87	$150.85	$150.90
Purchase #5	$95.67	10.320%	$105.5431	$105.54	$105.55	$105.50
Purchase #6	$24.72	4.246%	$25.7696	$25.77	$25.75	$25.80
Purchase #7	$52.36	4.315%	$54.6193	$54.62	$54.60	$54.60
7 purchase totals =	$924.96		$990.9596	$990.97	$990.95	$990.90