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	$160.34	6.275%	$170.4013	$170.40	$170.40	$170.40
Purchase #2	$100.62	10.823%	$111.5101	$111.51	$111.50	$111.50
Purchase #3	$197.65	12.610%	$222.5737	$222.57	$222.55	$222.60
Purchase #4	$213.44	7.569%	$229.5953	$229.60	$229.60	$229.60
Purchase #5	$91.51	4.536%	$95.6609	$95.66	$95.65	$95.70
Purchase #6	$240.91	6.115%	$255.6416	$255.64	$255.65	$255.60
Purchase #7	$81.56	11.699%	$91.1017	$91.10	$91.10	$91.10
7 purchase totals =	$1,086.03		$1,176.4846	$1,176.48	$1,176.45	$1,176.50