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	$190.64	13.748%	$216.8492	$216.85	$216.85	$216.80
Purchase #2	$200.52	10.828%	$222.2323	$222.23	$222.25	$222.20
Purchase #3	$204.74	9.316%	$223.8136	$223.81	$223.80	$223.80
Purchase #4	$63.40	12.406%	$71.2654	$71.27	$71.25	$71.30
Purchase #5	$101.89	3.437%	$105.392	$105.39	$105.40	$105.40
Purchase #6	$139.28	3.151%	$143.6687	$143.67	$143.65	$143.70
Purchase #7	$6.89	3.218%	$7.1117	$7.11	$7.10	$7.10
7 purchase totals =	$907.36		$990.3329	$990.33	$990.30	$990.30