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	$74.29	6.142%	$78.8529	$78.85	$78.85	$78.90
Purchase #2	$61.97	13.650%	$70.4289	$70.43	$70.45	$70.40
Purchase #3	$95.99	5.153%	$100.9364	$100.94	$100.95	$100.90
Purchase #4	$186.84	4.153%	$194.5995	$194.60	$194.60	$194.60
Purchase #5	$105.67	6.155%	$112.174	$112.17	$112.15	$112.20
Purchase #6	$118.64	12.469%	$133.4332	$133.43	$133.45	$133.40
Purchase #7	$220.78	9.722%	$242.2442	$242.24	$242.25	$242.20
7 purchase totals =	$864.18		$932.6691	$932.66	$932.70	$932.60