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	$211.39	13.188%	$239.2681	$239.27	$239.25	$239.30
Purchase #2	$43.27	6.666%	$46.1544	$46.15	$46.15	$46.20
Purchase #3	$45.58	12.679%	$51.3591	$51.36	$51.35	$51.40
Purchase #4	$189.53	10.285%	$209.0232	$209.02	$209.00	$209.00
Purchase #5	$44.52	4.377%	$46.4686	$46.47	$46.45	$46.50
Purchase #6	$134.25	4.187%	$139.871	$139.87	$139.85	$139.90
Purchase #7	$221.41	11.182%	$246.1681	$246.17	$246.15	$246.20
7 purchase totals =	$889.95		$978.3125	$978.31	$978.20	$978.50