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	$69.70	12.159%	$78.1748	$78.17	$78.15	$78.20
Purchase #2	$79.44	4.634%	$83.1212	$83.12	$83.10	$83.10
Purchase #3	$183.69	3.636%	$190.369	$190.37	$190.35	$190.40
Purchase #4	$196.42	10.854%	$217.7394	$217.74	$217.75	$217.70
Purchase #5	$74.68	4.635%	$78.1414	$78.14	$78.15	$78.10
Purchase #6	$211.67	8.596%	$229.8652	$229.87	$229.85	$229.90
Purchase #7	$59.74	5.102%	$62.7879	$62.79	$62.80	$62.80
7 purchase totals =	$875.34		$940.1989	$940.20	$940.15	$940.20