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	$106.40	11.191%	$118.3072	$118.31	$118.30	$118.30
Purchase #2	$159.90	6.836%	$170.8308	$170.83	$170.85	$170.80
Purchase #3	$222.30	3.855%	$230.8697	$230.87	$230.85	$230.90
Purchase #4	$210.93	10.647%	$233.3877	$233.39	$233.40	$233.40
Purchase #5	$145.81	10.770%	$161.5137	$161.51	$161.50	$161.50
Purchase #6	$141.45	6.158%	$150.1605	$150.16	$150.15	$150.20
Purchase #7	$16.81	9.282%	$18.3703	$18.37	$18.35	$18.40
7 purchase totals =	$1,003.60		$1,083.4399	$1,083.44	$1,083.40	$1,083.50