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	$227.97	6.840%	$243.5631	$243.56	$243.55	$243.60
Purchase #2	$80.46	8.848%	$87.5791	$87.58	$87.60	$87.60
Purchase #3	$126.78	11.410%	$141.2456	$141.25	$141.25	$141.20
Purchase #4	$177.52	10.801%	$196.6939	$196.69	$196.70	$196.70
Purchase #5	$81.72	8.704%	$88.8329	$88.83	$88.85	$88.80
Purchase #6	$165.49	6.442%	$176.1509	$176.15	$176.15	$176.20
Purchase #7	$106.31	4.533%	$111.129	$111.13	$111.15	$111.10
7 purchase totals =	$966.25		$1,045.1945	$1,045.19	$1,045.25	$1,045.20