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	$52.66	8.519%	$57.1461	$57.15	$57.15	$57.10
Purchase #2	$45.51	5.838%	$48.1669	$48.17	$48.15	$48.20
Purchase #3	$48.31	4.656%	$50.5593	$50.56	$50.55	$50.60
Purchase #4	$64.88	13.264%	$73.4857	$73.49	$73.50	$73.50
Purchase #5	$21.82	10.721%	$24.1593	$24.16	$24.15	$24.20
Purchase #6	$48.25	4.726%	$50.5303	$50.53	$50.55	$50.50
Purchase #7	$99.49	11.780%	$111.2099	$111.21	$111.20	$111.20
7 purchase totals =	$380.92		$415.2575	$415.27	$415.25	$415.30