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	$117.91	7.181%	$126.3771	$126.38	$126.40	$126.40
Purchase #2	$235.32	11.564%	$262.5324	$262.53	$262.55	$262.50
Purchase #3	$111.37	10.874%	$123.4804	$123.48	$123.50	$123.50
Purchase #4	$116.28	8.537%	$126.2068	$126.21	$126.20	$126.20
Purchase #5	$169.41	12.229%	$190.1271	$190.13	$190.15	$190.10
Purchase #6	$36.44	8.611%	$39.5778	$39.58	$39.60	$39.60
Purchase #7	$220.44	4.194%	$229.6853	$229.69	$229.70	$229.70
7 purchase totals =	$1,007.17		$1,097.9869	$1,098.00	$1,098.10	$1,098.00