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	$217.36	10.273%	$239.6894	$239.69	$239.70	$239.70
Purchase #2	$59.78	6.329%	$63.5635	$63.56	$63.55	$63.60
Purchase #3	$233.46	13.247%	$264.3864	$264.39	$264.40	$264.40
Purchase #4	$20.87	3.737%	$21.6499	$21.65	$21.65	$21.60
Purchase #5	$42.38	12.308%	$47.5961	$47.60	$47.60	$47.60
Purchase #6	$82.70	9.316%	$90.4043	$90.40	$90.40	$90.40
Purchase #7	$223.70	13.418%	$253.7161	$253.72	$253.70	$253.70
7 purchase totals =	$880.25		$981.0057	$981.01	$981.00	$981.00