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	$220.67	11.342%	$245.6984	$245.70	$245.70	$245.70
Purchase #2	$112.41	5.763%	$118.8882	$118.89	$118.90	$118.90
Purchase #3	$85.98	4.549%	$89.8912	$89.89	$89.90	$89.90
Purchase #4	$222.66	7.174%	$238.6336	$238.63	$238.65	$238.60
Purchase #5	$29.57	10.266%	$32.6057	$32.61	$32.60	$32.60
Purchase #6	$130.76	9.519%	$143.207	$143.21	$143.20	$143.20
Purchase #7	$84.36	7.193%	$90.428	$90.43	$90.45	$90.40
7 purchase totals =	$886.41		$959.3521	$959.36	$959.40	$959.30