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	$106.85	11.555%	$119.1965	$119.20	$119.20	$119.20
Purchase #2	$108.30	6.323%	$115.1478	$115.15	$115.15	$115.10
Purchase #3	$86.40	10.472%	$95.4478	$95.45	$95.45	$95.40
Purchase #4	$127.67	12.368%	$143.4602	$143.46	$143.45	$143.50
Purchase #5	$190.66	12.560%	$214.6069	$214.61	$214.60	$214.60
Purchase #6	$12.33	8.404%	$13.3662	$13.37	$13.35	$13.40
Purchase #7	$139.92	13.118%	$158.2747	$158.27	$158.25	$158.30
7 purchase totals =	$772.13		$859.5001	$859.51	$859.45	$859.50