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	$130.50	6.105%	$138.467	$138.47	$138.45	$138.50
Purchase #2	$112.96	5.636%	$119.3264	$119.33	$119.35	$119.30
Purchase #3	$90.45	13.424%	$102.592	$102.59	$102.60	$102.60
Purchase #4	$126.87	12.830%	$143.1474	$143.15	$143.15	$143.10
Purchase #5	$18.35	9.246%	$20.0466	$20.05	$20.05	$20.00
Purchase #6	$101.70	12.499%	$114.4115	$114.41	$114.40	$114.40
Purchase #7	$227.95	4.653%	$238.5565	$238.56	$238.55	$238.60
7 purchase totals =	$808.78		$876.5474	$876.56	$876.55	$876.50