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	$244.47	4.465%	$255.3856	$255.39	$255.40	$255.40
Purchase #2	$119.55	9.806%	$131.2731	$131.27	$131.25	$131.30
Purchase #3	$148.87	13.812%	$169.4319	$169.43	$169.45	$169.40
Purchase #4	$200.69	12.822%	$226.4225	$226.42	$226.40	$226.40
Purchase #5	$246.71	12.638%	$277.8892	$277.89	$277.90	$277.90
Purchase #6	$89.78	10.537%	$99.2401	$99.24	$99.25	$99.20
Purchase #7	$139.81	6.169%	$148.4349	$148.43	$148.45	$148.40
7 purchase totals =	$1,189.88		$1,308.0773	$1,308.07	$1,308.10	$1,308.00