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	$235.43	12.332%	$264.4632	$264.46	$264.45	$264.50
Purchase #2	$233.88	9.693%	$256.55	$256.55	$256.55	$256.60
Purchase #3	$158.88	10.307%	$175.2558	$175.26	$175.25	$175.30
Purchase #4	$145.82	12.266%	$163.7063	$163.71	$163.70	$163.70
Purchase #5	$76.97	8.177%	$83.2638	$83.26	$83.25	$83.30
Purchase #6	$102.46	9.163%	$111.8484	$111.85	$111.85	$111.80
Purchase #7	$63.59	13.195%	$71.9807	$71.98	$72.00	$72.00
7 purchase totals =	$1,017.03		$1,127.0682	$1,127.07	$1,127.05	$1,127.20