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	$103.78	4.594%	$108.5477	$108.55	$108.55	$108.50
Purchase #2	$50.48	11.839%	$56.4563	$56.46	$56.45	$56.50
Purchase #3	$115.37	5.131%	$121.2896	$121.29	$121.30	$121.30
Purchase #4	$46.89	13.588%	$53.2614	$53.26	$53.25	$53.30
Purchase #5	$127.40	13.391%	$144.4601	$144.46	$144.45	$144.50
Purchase #6	$156.82	9.730%	$172.0786	$172.08	$172.10	$172.10
Purchase #7	$223.79	13.314%	$253.5854	$253.59	$253.60	$253.60
7 purchase totals =	$824.53		$909.6791	$909.69	$909.70	$909.80