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	$233.91	5.121%	$245.8885	$245.89	$245.90	$245.90
Purchase #2	$198.70	11.335%	$221.2226	$221.22	$221.20	$221.20
Purchase #3	$98.97	12.617%	$111.457	$111.46	$111.45	$111.50
Purchase #4	$11.87	9.663%	$13.017	$13.02	$13.00	$13.00
Purchase #5	$139.79	6.378%	$148.7058	$148.71	$148.70	$148.70
Purchase #6	$38.43	10.645%	$42.5209	$42.52	$42.50	$42.50
Purchase #7	$20.37	13.509%	$23.1218	$23.12	$23.10	$23.10
7 purchase totals =	$742.04		$805.9336	$805.94	$805.85	$805.90