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	$92.37	8.811%	$100.5087	$100.51	$100.50	$100.50
Purchase #2	$44.61	8.488%	$48.3965	$48.40	$48.40	$48.40
Purchase #3	$192.76	11.786%	$215.4787	$215.48	$215.50	$215.50
Purchase #4	$76.70	8.826%	$83.4695	$83.47	$83.45	$83.50
Purchase #5	$58.39	13.297%	$66.1541	$66.15	$66.15	$66.20
Purchase #6	$204.64	11.210%	$227.5801	$227.58	$227.60	$227.60
Purchase #7	$176.52	11.502%	$196.8233	$196.82	$196.80	$196.80
7 purchase totals =	$845.99		$938.4109	$938.41	$938.40	$938.50