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	$65.25	3.517%	$67.5448	$67.54	$67.55	$67.50
Purchase #2	$192.27	9.603%	$210.7337	$210.73	$210.75	$210.70
Purchase #3	$239.75	4.113%	$249.6109	$249.61	$249.60	$249.60
Purchase #4	$100.28	11.593%	$111.9055	$111.91	$111.90	$111.90
Purchase #5	$106.89	8.685%	$116.1734	$116.17	$116.15	$116.20
Purchase #6	$181.43	12.142%	$203.4592	$203.46	$203.45	$203.50
Purchase #7	$26.73	8.643%	$29.0403	$29.04	$29.05	$29.00
7 purchase totals =	$912.60		$988.4678	$988.46	$988.45	$988.40