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	$42.68	8.212%	$46.1849	$46.18	$46.20	$46.20
Purchase #2	$102.89	8.342%	$111.4731	$111.47	$111.45	$111.50
Purchase #3	$9.81	13.235%	$11.1084	$11.11	$11.10	$11.10
Purchase #4	$225.33	10.357%	$248.6674	$248.67	$248.65	$248.70
Purchase #5	$42.30	11.782%	$47.2838	$47.28	$47.30	$47.30
Purchase #6	$32.35	6.411%	$34.424	$34.42	$34.40	$34.40
Purchase #7	$54.64	8.779%	$59.4368	$59.44	$59.45	$59.40
7 purchase totals =	$510.00		$558.5784	$558.57	$558.55	$558.60