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	$12.25	8.757%	$13.3227	$13.32	$13.30	$13.30
Purchase #2	$57.71	6.451%	$61.4329	$61.43	$61.45	$61.40
Purchase #3	$174.58	11.447%	$194.5642	$194.56	$194.55	$194.60
Purchase #4	$113.93	6.159%	$120.9469	$120.95	$120.95	$120.90
Purchase #5	$95.34	10.682%	$105.5242	$105.52	$105.50	$105.50
Purchase #6	$168.40	13.239%	$190.6945	$190.69	$190.70	$190.70
Purchase #7	$227.57	5.689%	$240.5165	$240.52	$240.50	$240.50
7 purchase totals =	$849.78		$927.0019	$926.99	$926.95	$926.90