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	$172.79	4.401%	$180.3945	$180.39	$180.40	$180.40
Purchase #2	$203.68	5.809%	$215.5118	$215.51	$215.50	$215.50
Purchase #3	$166.38	11.291%	$185.166	$185.17	$185.15	$185.20
Purchase #4	$52.74	13.636%	$59.9316	$59.93	$59.95	$59.90
Purchase #5	$107.47	8.637%	$116.7522	$116.75	$116.75	$116.80
Purchase #6	$35.95	10.443%	$39.7043	$39.70	$39.70	$39.70
Purchase #7	$59.61	5.359%	$62.8045	$62.80	$62.80	$62.80
7 purchase totals =	$798.62		$860.2649	$860.25	$860.25	$860.30