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	$239.78	13.382%	$271.8674	$271.87	$271.85	$271.90
Purchase #2	$61.65	9.384%	$67.4352	$67.44	$67.45	$67.40
Purchase #3	$135.25	3.485%	$139.9635	$139.96	$139.95	$140.00
Purchase #4	$91.42	10.347%	$100.8792	$100.88	$100.90	$100.90
Purchase #5	$145.82	4.242%	$152.0057	$152.01	$152.00	$152.00
Purchase #6	$136.60	8.170%	$147.7602	$147.76	$147.75	$147.80
Purchase #7	$125.90	13.705%	$143.1546	$143.15	$143.15	$143.20
7 purchase totals =	$936.42		$1,023.0658	$1,023.07	$1,023.05	$1,023.20