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	$95.68	13.722%	$108.8092	$108.81	$108.80	$108.80
Purchase #2	$171.35	7.836%	$184.777	$184.78	$184.80	$184.80
Purchase #3	$174.97	9.221%	$191.104	$191.10	$191.10	$191.10
Purchase #4	$194.60	3.116%	$200.6637	$200.66	$200.65	$200.70
Purchase #5	$83.39	8.530%	$90.5032	$90.50	$90.50	$90.50
Purchase #6	$32.45	11.843%	$36.2931	$36.29	$36.30	$36.30
Purchase #7	$94.37	5.866%	$99.9057	$99.91	$99.90	$99.90
7 purchase totals =	$846.81		$912.0559	$912.05	$912.05	$912.10