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	$40.45	3.776%	$41.9774	$41.98	$42.00	$42.00
Purchase #2	$153.81	9.154%	$167.8898	$167.89	$167.90	$167.90
Purchase #3	$175.98	10.767%	$194.9278	$194.93	$194.95	$194.90
Purchase #4	$88.50	7.784%	$95.3888	$95.39	$95.40	$95.40
Purchase #5	$34.67	13.823%	$39.4624	$39.46	$39.45	$39.50
Purchase #6	$188.42	5.291%	$198.3893	$198.39	$198.40	$198.40
Purchase #7	$105.79	7.864%	$114.1093	$114.11	$114.10	$114.10
7 purchase totals =	$787.62		$852.1448	$852.15	$852.20	$852.20