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	$59.31	13.178%	$67.1259	$67.13	$67.15	$67.10
Purchase #2	$132.78	9.725%	$145.6929	$145.69	$145.70	$145.70
Purchase #3	$19.86	7.663%	$21.3819	$21.38	$21.40	$21.40
Purchase #4	$117.45	13.672%	$133.5078	$133.51	$133.50	$133.50
Purchase #5	$83.82	7.422%	$90.0411	$90.04	$90.05	$90.00
Purchase #6	$103.38	7.107%	$110.7272	$110.73	$110.75	$110.70
Purchase #7	$121.85	10.108%	$134.1666	$134.17	$134.15	$134.20
7 purchase totals =	$638.45		$702.6434	$702.65	$702.70	$702.60