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	$250.97	13.396%	$284.5899	$284.59	$284.60	$284.60
Purchase #2	$89.58	11.282%	$99.6864	$99.69	$99.70	$99.70
Purchase #3	$128.72	8.575%	$139.7577	$139.76	$139.75	$139.80
Purchase #4	$61.96	6.746%	$66.1398	$66.14	$66.15	$66.10
Purchase #5	$75.52	4.235%	$78.7183	$78.72	$78.70	$78.70
Purchase #6	$220.94	10.495%	$244.1277	$244.13	$244.15	$244.10
Purchase #7	$219.92	7.202%	$235.7586	$235.76	$235.75	$235.80
7 purchase totals =	$1,047.61		$1,148.7784	$1,148.79	$1,148.80	$1,148.80