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	$199.54	13.121%	$225.7216	$225.72	$225.70	$225.70
Purchase #2	$34.87	11.707%	$38.9522	$38.95	$38.95	$39.00
Purchase #3	$104.72	5.494%	$110.4733	$110.47	$110.45	$110.50
Purchase #4	$128.56	12.467%	$144.5876	$144.59	$144.60	$144.60
Purchase #5	$78.31	5.706%	$82.7784	$82.78	$82.80	$82.80
Purchase #6	$19.80	6.696%	$21.1258	$21.13	$21.15	$21.10
Purchase #7	$221.54	4.471%	$231.4451	$231.45	$231.45	$231.40
7 purchase totals =	$787.34		$855.0840	$855.09	$855.10	$855.10