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	$29.60	7.497%	$31.8191	$31.82	$31.80	$31.80
Purchase #2	$58.49	13.783%	$66.5517	$66.55	$66.55	$66.60
Purchase #3	$173.40	10.405%	$191.4423	$191.44	$191.45	$191.40
Purchase #4	$240.54	10.671%	$266.208	$266.21	$266.20	$266.20
Purchase #5	$75.72	8.865%	$82.4326	$82.43	$82.45	$82.40
Purchase #6	$171.46	8.437%	$185.9261	$185.93	$185.95	$185.90
Purchase #7	$166.94	3.421%	$172.651	$172.65	$172.65	$172.70
7 purchase totals =	$916.15		$997.0308	$997.03	$997.05	$997.00