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	$19.98	9.434%	$21.8649	$21.86	$21.85	$21.90
Purchase #2	$74.82	3.347%	$77.3242	$77.32	$77.30	$77.30
Purchase #3	$80.67	11.114%	$89.6357	$89.64	$89.65	$89.60
Purchase #4	$91.94	12.390%	$103.3314	$103.33	$103.35	$103.30
Purchase #5	$147.99	7.741%	$159.4459	$159.45	$159.45	$159.40
Purchase #6	$216.58	8.793%	$235.6239	$235.62	$235.60	$235.60
Purchase #7	$51.60	6.406%	$54.9055	$54.91	$54.90	$54.90
7 purchase totals =	$683.58		$742.1315	$742.13	$742.10	$742.00