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	$49.97	5.420%	$52.6784	$52.68	$52.70	$52.70
Purchase #2	$181.98	4.161%	$189.5522	$189.55	$189.55	$189.60
Purchase #3	$80.76	6.507%	$86.0151	$86.02	$86.00	$86.00
Purchase #4	$40.74	12.638%	$45.8887	$45.89	$45.90	$45.90
Purchase #5	$61.98	11.121%	$68.8728	$68.87	$68.85	$68.90
Purchase #6	$77.93	9.650%	$85.4502	$85.45	$85.45	$85.50
Purchase #7	$106.52	10.862%	$118.0902	$118.09	$118.10	$118.10
7 purchase totals =	$599.88		$646.5476	$646.55	$646.55	$646.70