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	$89.98	11.430%	$100.2647	$100.26	$100.25	$100.30
Purchase #2	$73.27	8.552%	$79.5361	$79.54	$79.55	$79.50
Purchase #3	$12.39	6.216%	$13.1602	$13.16	$13.15	$13.20
Purchase #4	$221.45	13.635%	$251.6447	$251.64	$251.65	$251.60
Purchase #5	$108.85	7.792%	$117.3316	$117.33	$117.35	$117.30
Purchase #6	$19.87	3.475%	$20.5605	$20.56	$20.55	$20.60
Purchase #7	$49.27	10.687%	$54.5355	$54.54	$54.55	$54.50
7 purchase totals =	$575.08		$637.0333	$637.03	$637.05	$637.00