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	$12.84	7.139%	$13.7566	$13.76	$13.75	$13.80
Purchase #2	$151.85	10.572%	$167.9036	$167.90	$167.90	$167.90
Purchase #3	$64.64	9.752%	$70.9437	$70.94	$70.95	$70.90
Purchase #4	$196.38	13.273%	$222.4455	$222.45	$222.45	$222.40
Purchase #5	$130.62	4.724%	$136.7905	$136.79	$136.80	$136.80
Purchase #6	$146.89	13.692%	$167.0022	$167.00	$167.00	$167.00
Purchase #7	$129.83	9.843%	$142.6092	$142.61	$142.60	$142.60
7 purchase totals =	$833.05		$921.4513	$921.45	$921.45	$921.40