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	$140.93	9.195%	$153.8885	$153.89	$153.90	$153.90
Purchase #2	$177.67	12.317%	$199.5536	$199.55	$199.55	$199.60
Purchase #3	$108.67	10.747%	$120.3488	$120.35	$120.35	$120.30
Purchase #4	$111.59	7.285%	$119.7193	$119.72	$119.70	$119.70
Purchase #5	$85.25	4.486%	$89.0743	$89.07	$89.05	$89.10
Purchase #6	$6.33	13.868%	$7.2078	$7.21	$7.20	$7.20
Purchase #7	$188.47	13.599%	$214.1	$214.10	$214.10	$214.10
7 purchase totals =	$818.91		$903.8923	$903.89	$903.85	$903.90