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	$155.99	12.104%	$174.871	$174.87	$174.85	$174.90
Purchase #2	$15.94	9.662%	$17.4801	$17.48	$17.50	$17.50
Purchase #3	$13.29	3.267%	$13.7242	$13.72	$13.70	$13.70
Purchase #4	$167.45	7.414%	$179.8647	$179.86	$179.85	$179.90
Purchase #5	$18.85	4.768%	$19.7488	$19.75	$19.75	$19.70
Purchase #6	$154.47	11.856%	$172.784	$172.78	$172.80	$172.80
Purchase #7	$176.57	4.857%	$185.146	$185.15	$185.15	$185.10
7 purchase totals =	$702.56		$763.6188	$763.61	$763.60	$763.60