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	$99.46	4.429%	$103.8651	$103.87	$103.85	$103.90
Purchase #2	$76.78	12.819%	$86.6224	$86.62	$86.60	$86.60
Purchase #3	$39.69	3.365%	$41.0256	$41.03	$41.05	$41.00
Purchase #4	$135.58	10.595%	$149.9447	$149.94	$149.95	$149.90
Purchase #5	$68.99	3.592%	$71.4681	$71.47	$71.45	$71.50
Purchase #6	$133.57	11.245%	$148.5899	$148.59	$148.60	$148.60
Purchase #7	$48.72	7.619%	$52.432	$52.43	$52.45	$52.40
7 purchase totals =	$602.79		$653.9478	$653.95	$653.95	$653.90