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	$77.91	7.561%	$83.8008	$83.80	$83.80	$83.80
Purchase #2	$18.48	10.841%	$20.4834	$20.48	$20.50	$20.50
Purchase #3	$37.81	7.593%	$40.6809	$40.68	$40.70	$40.70
Purchase #4	$209.33	6.724%	$223.4053	$223.41	$223.40	$223.40
Purchase #5	$124.80	12.411%	$140.2889	$140.29	$140.30	$140.30
Purchase #6	$233.88	10.442%	$258.3017	$258.30	$258.30	$258.30
Purchase #7	$87.67	6.466%	$93.3387	$93.34	$93.35	$93.30
7 purchase totals =	$789.88		$860.2997	$860.30	$860.35	$860.30