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	$87.71	13.162%	$99.2544	$99.25	$99.25	$99.30
Purchase #2	$155.50	10.726%	$172.1789	$172.18	$172.20	$172.20
Purchase #3	$110.97	12.258%	$124.5727	$124.57	$124.55	$124.60
Purchase #4	$48.59	4.136%	$50.5997	$50.60	$50.60	$50.60
Purchase #5	$212.53	5.326%	$223.8493	$223.85	$223.85	$223.80
Purchase #6	$121.93	8.639%	$132.4635	$132.46	$132.45	$132.50
Purchase #7	$81.61	10.531%	$90.2043	$90.20	$90.20	$90.20
7 purchase totals =	$818.84		$893.1228	$893.11	$893.10	$893.20