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	$202.89	6.667%	$216.4167	$216.42	$216.40	$216.40
Purchase #2	$106.90	4.593%	$111.8099	$111.81	$111.80	$111.80
Purchase #3	$90.28	11.764%	$100.9005	$100.90	$100.90	$100.90
Purchase #4	$139.35	6.747%	$148.7519	$148.75	$148.75	$148.80
Purchase #5	$27.71	9.208%	$30.2615	$30.26	$30.25	$30.30
Purchase #6	$159.37	8.384%	$172.7316	$172.73	$172.75	$172.70
Purchase #7	$20.39	3.187%	$21.0398	$21.04	$21.05	$21.00
7 purchase totals =	$746.89		$801.9119	$801.91	$801.90	$801.90