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	$181.60	4.844%	$190.3967	$190.40	$190.40	$190.40
Purchase #2	$234.56	5.491%	$247.4397	$247.44	$247.45	$247.40
Purchase #3	$133.53	10.148%	$147.0806	$147.08	$147.10	$147.10
Purchase #4	$105.98	10.255%	$116.8482	$116.85	$116.85	$116.80
Purchase #5	$235.59	5.762%	$249.1647	$249.16	$249.15	$249.20
Purchase #6	$216.44	11.628%	$241.6076	$241.61	$241.60	$241.60
Purchase #7	$45.97	10.709%	$50.8929	$50.89	$50.90	$50.90
7 purchase totals =	$1,153.67		$1,243.4304	$1,243.43	$1,243.45	$1,243.40