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	$242.78	5.643%	$256.4801	$256.48	$256.50	$256.50
Purchase #2	$222.98	4.325%	$232.6239	$232.62	$232.60	$232.60
Purchase #3	$177.48	10.429%	$195.9894	$195.99	$196.00	$196.00
Purchase #4	$54.88	8.617%	$59.609	$59.61	$59.60	$59.60
Purchase #5	$181.34	5.617%	$191.5259	$191.53	$191.55	$191.50
Purchase #6	$55.35	7.439%	$59.4675	$59.47	$59.45	$59.50
Purchase #7	$8.69	13.478%	$9.8612	$9.86	$9.85	$9.90
7 purchase totals =	$943.50		$1,005.5570	$1,005.56	$1,005.55	$1,005.60