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	$47.89	13.437%	$54.325	$54.33	$54.35	$54.30
Purchase #2	$183.55	6.856%	$196.1342	$196.13	$196.15	$196.10
Purchase #3	$217.52	4.642%	$227.6173	$227.62	$227.60	$227.60
Purchase #4	$158.47	9.409%	$173.3804	$173.38	$173.40	$173.40
Purchase #5	$17.65	10.211%	$19.4522	$19.45	$19.45	$19.50
Purchase #6	$151.78	6.294%	$161.333	$161.33	$161.35	$161.30
Purchase #7	$239.85	3.772%	$248.8971	$248.90	$248.90	$248.90
7 purchase totals =	$1,016.71		$1,081.1392	$1,081.14	$1,081.20	$1,081.10