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	$225.39	3.631%	$233.5739	$233.57	$233.55	$233.60
Purchase #2	$160.67	9.845%	$176.488	$176.49	$176.50	$176.50
Purchase #3	$243.74	5.637%	$257.4796	$257.48	$257.50	$257.50
Purchase #4	$123.56	13.215%	$139.8885	$139.89	$139.90	$139.90
Purchase #5	$47.75	8.260%	$51.6942	$51.69	$51.70	$51.70
Purchase #6	$123.39	11.634%	$137.7452	$137.75	$137.75	$137.70
Purchase #7	$75.60	3.378%	$78.1538	$78.15	$78.15	$78.20
7 purchase totals =	$1,000.10		$1,075.0232	$1,075.02	$1,075.05	$1,075.10