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	$112.88	3.202%	$116.4944	$116.49	$116.50	$116.50
Purchase #2	$136.90	11.792%	$153.0432	$153.04	$153.05	$153.00
Purchase #3	$89.91	10.615%	$99.4539	$99.45	$99.45	$99.50
Purchase #4	$41.68	13.854%	$47.4543	$47.45	$47.45	$47.50
Purchase #5	$18.47	5.245%	$19.4388	$19.44	$19.45	$19.40
Purchase #6	$154.54	9.584%	$169.3511	$169.35	$169.35	$169.40
Purchase #7	$36.68	6.724%	$39.1464	$39.15	$39.15	$39.10
7 purchase totals =	$591.06		$644.3821	$644.37	$644.40	$644.40