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	$190.55	10.276%	$210.1309	$210.13	$210.15	$210.10
Purchase #2	$145.74	13.842%	$165.9133	$165.91	$165.90	$165.90
Purchase #3	$107.51	3.361%	$111.1234	$111.12	$111.10	$111.10
Purchase #4	$37.31	9.412%	$40.8216	$40.82	$40.80	$40.80
Purchase #5	$241.33	10.585%	$266.8748	$266.87	$266.85	$266.90
Purchase #6	$19.67	7.256%	$21.0973	$21.10	$21.10	$21.10
Purchase #7	$144.87	6.615%	$154.4532	$154.45	$154.45	$154.50
7 purchase totals =	$886.98		$970.4145	$970.40	$970.35	$970.40