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	$19.95	9.158%	$21.777	$21.78	$21.80	$21.80
Purchase #2	$30.92	6.428%	$32.9075	$32.91	$32.90	$32.90
Purchase #3	$128.98	7.395%	$138.5181	$138.52	$138.50	$138.50
Purchase #4	$80.43	4.332%	$83.9142	$83.91	$83.90	$83.90
Purchase #5	$93.84	6.514%	$99.9527	$99.95	$99.95	$100.00
Purchase #6	$52.35	13.350%	$59.3387	$59.34	$59.35	$59.30
Purchase #7	$101.63	9.422%	$111.2056	$111.21	$111.20	$111.20
7 purchase totals =	$508.10		$547.6138	$547.62	$547.60	$547.60