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	$45.59	9.359%	$49.8568	$49.86	$49.85	$49.90
Purchase #2	$34.94	4.329%	$36.4526	$36.45	$36.45	$36.50
Purchase #3	$59.53	9.433%	$65.1455	$65.15	$65.15	$65.10
Purchase #4	$99.85	5.295%	$105.1371	$105.14	$105.15	$105.10
Purchase #5	$133.39	6.778%	$142.4312	$142.43	$142.45	$142.40
Purchase #6	$40.67	10.299%	$44.8586	$44.86	$44.85	$44.90
Purchase #7	$49.60	10.324%	$54.7207	$54.72	$54.70	$54.70
7 purchase totals =	$463.57		$498.6025	$498.61	$498.60	$498.60