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	$97.66	6.124%	$103.6407	$103.64	$103.65	$103.60
Purchase #2	$63.76	11.798%	$71.2824	$71.28	$71.30	$71.30
Purchase #3	$152.59	10.564%	$168.7096	$168.71	$168.70	$168.70
Purchase #4	$16.93	6.389%	$18.0117	$18.01	$18.00	$18.00
Purchase #5	$216.59	3.123%	$223.3541	$223.35	$223.35	$223.40
Purchase #6	$56.98	4.395%	$59.4843	$59.48	$59.50	$59.50
Purchase #7	$116.95	11.254%	$130.1116	$130.11	$130.10	$130.10
7 purchase totals =	$721.46		$774.5944	$774.58	$774.60	$774.60