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	$149.79	12.872%	$169.071	$169.07	$169.05	$169.10
Purchase #2	$157.38	9.581%	$172.4586	$172.46	$172.45	$172.50
Purchase #3	$230.29	11.550%	$256.8885	$256.89	$256.90	$256.90
Purchase #4	$172.49	10.637%	$190.8378	$190.84	$190.85	$190.80
Purchase #5	$229.25	6.361%	$243.8326	$243.83	$243.85	$243.80
Purchase #6	$30.49	7.113%	$32.6588	$32.66	$32.65	$32.70
Purchase #7	$243.40	5.829%	$257.5878	$257.59	$257.60	$257.60
7 purchase totals =	$1,213.09		$1,323.3351	$1,323.34	$1,323.35	$1,323.40