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	$54.27	5.246%	$57.117	$57.12	$57.10	$57.10
Purchase #2	$220.30	8.272%	$238.5232	$238.52	$238.50	$238.50
Purchase #3	$208.45	3.396%	$215.529	$215.53	$215.55	$215.50
Purchase #4	$141.65	6.710%	$151.1547	$151.15	$151.15	$151.20
Purchase #5	$57.86	9.752%	$63.5025	$63.50	$63.50	$63.50
Purchase #6	$203.47	13.557%	$231.0544	$231.05	$231.05	$231.10
Purchase #7	$20.79	4.484%	$21.7222	$21.72	$21.70	$21.70
7 purchase totals =	$906.79		$978.6030	$978.59	$978.55	$978.60