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	$99.58	12.292%	$111.8204	$111.82	$111.80	$111.80
Purchase #2	$49.27	7.321%	$52.8771	$52.88	$52.90	$52.90
Purchase #3	$103.34	4.559%	$108.0513	$108.05	$108.05	$108.10
Purchase #4	$139.87	7.307%	$150.0903	$150.09	$150.10	$150.10
Purchase #5	$204.89	11.836%	$229.1408	$229.14	$229.15	$229.10
Purchase #6	$5.33	5.467%	$5.6214	$5.62	$5.60	$5.60
Purchase #7	$155.90	4.804%	$163.3894	$163.39	$163.40	$163.40
7 purchase totals =	$758.18		$820.9907	$820.99	$821.00	$821.00