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	$62.36	12.818%	$70.3533	$70.35	$70.35	$70.40
Purchase #2	$117.61	7.497%	$126.4272	$126.43	$126.45	$126.40
Purchase #3	$38.31	11.643%	$42.7704	$42.77	$42.75	$42.80
Purchase #4	$27.89	7.831%	$30.0741	$30.07	$30.05	$30.10
Purchase #5	$52.59	3.164%	$54.2539	$54.25	$54.25	$54.30
Purchase #6	$97.60	6.263%	$103.7127	$103.71	$103.70	$103.70
Purchase #7	$92.65	8.208%	$100.2547	$100.25	$100.25	$100.30
7 purchase totals =	$489.01		$527.8463	$527.83	$527.80	$528.00