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	$246.35	5.862%	$260.791	$260.79	$260.80	$260.80
Purchase #2	$106.70	3.661%	$110.6063	$110.61	$110.60	$110.60
Purchase #3	$135.81	10.450%	$150.0021	$150.00	$150.00	$150.00
Purchase #4	$239.65	13.783%	$272.681	$272.68	$272.70	$272.70
Purchase #5	$150.43	11.563%	$167.8242	$167.82	$167.80	$167.80
Purchase #6	$47.39	4.565%	$49.5534	$49.55	$49.55	$49.60
Purchase #7	$98.76	13.122%	$111.7193	$111.72	$111.70	$111.70
7 purchase totals =	$1,025.09		$1,123.1773	$1,123.17	$1,123.15	$1,123.20