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	$59.95	3.313%	$61.9361	$61.94	$61.95	$61.90
Purchase #2	$238.80	13.535%	$271.1216	$271.12	$271.10	$271.10
Purchase #3	$43.56	12.757%	$49.1169	$49.12	$49.10	$49.10
Purchase #4	$54.60	13.571%	$62.0098	$62.01	$62.00	$62.00
Purchase #5	$59.98	12.723%	$67.6113	$67.61	$67.60	$67.60
Purchase #6	$72.33	10.347%	$79.814	$79.81	$79.80	$79.80
Purchase #7	$103.58	5.324%	$109.0946	$109.09	$109.10	$109.10
7 purchase totals =	$632.80		$700.7043	$700.70	$700.65	$700.60