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	$28.83	4.565%	$30.1461	$30.15	$30.15	$30.10
Purchase #2	$33.96	9.671%	$37.2443	$37.24	$37.25	$37.20
Purchase #3	$45.71	6.592%	$48.7232	$48.72	$48.70	$48.70
Purchase #4	$29.70	12.396%	$33.3816	$33.38	$33.40	$33.40
Purchase #5	$108.64	5.337%	$114.4381	$114.44	$114.45	$114.40
Purchase #6	$40.52	13.536%	$46.0048	$46.00	$46.00	$46.00
Purchase #7	$6.72	13.623%	$7.6355	$7.64	$7.65	$7.60
7 purchase totals =	$294.08		$317.5736	$317.57	$317.60	$317.40