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	$52.70	10.775%	$58.3784	$58.38	$58.40	$58.40
Purchase #2	$126.69	3.509%	$131.1356	$131.14	$131.15	$131.10
Purchase #3	$98.94	5.713%	$104.5924	$104.59	$104.60	$104.60
Purchase #4	$39.43	6.742%	$42.0884	$42.09	$42.10	$42.10
Purchase #5	$195.38	5.126%	$205.3952	$205.40	$205.40	$205.40
Purchase #6	$10.72	6.861%	$11.4555	$11.46	$11.45	$11.50
Purchase #7	$116.45	10.176%	$128.3	$128.30	$128.30	$128.30
7 purchase totals =	$640.31		$681.3455	$681.36	$681.40	$681.40