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	$62.81	6.671%	$67.0001	$67.00	$67.00	$67.00
Purchase #2	$191.88	13.534%	$217.849	$217.85	$217.85	$217.80
Purchase #3	$111.98	3.106%	$115.4581	$115.46	$115.45	$115.50
Purchase #4	$82.31	8.664%	$89.4413	$89.44	$89.45	$89.40
Purchase #5	$100.98	7.720%	$108.7757	$108.78	$108.80	$108.80
Purchase #6	$112.98	9.805%	$124.0577	$124.06	$124.05	$124.10
Purchase #7	$59.49	9.318%	$65.0333	$65.03	$65.05	$65.00
7 purchase totals =	$722.43		$787.6152	$787.62	$787.65	$787.60