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	$30.27	13.509%	$34.3592	$34.36	$34.35	$34.40
Purchase #2	$62.33	10.872%	$69.1065	$69.11	$69.10	$69.10
Purchase #3	$56.71	8.737%	$61.6648	$61.66	$61.65	$61.70
Purchase #4	$187.52	4.725%	$196.3803	$196.38	$196.40	$196.40
Purchase #5	$50.87	7.266%	$54.5662	$54.57	$54.55	$54.60
Purchase #6	$17.95	13.287%	$20.335	$20.34	$20.35	$20.30
Purchase #7	$225.52	7.556%	$242.5603	$242.56	$242.55	$242.60
7 purchase totals =	$631.17		$678.9723	$678.98	$678.95	$679.10