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	$234.35	4.324%	$244.4833	$244.48	$244.50	$244.50
Purchase #2	$72.69	7.315%	$78.0073	$78.01	$78.00	$78.00
Purchase #3	$111.51	10.588%	$123.3167	$123.32	$123.30	$123.30
Purchase #4	$210.39	8.575%	$228.4309	$228.43	$228.45	$228.40
Purchase #5	$205.83	13.487%	$233.5903	$233.59	$233.60	$233.60
Purchase #6	$71.46	7.387%	$76.7388	$76.74	$76.75	$76.70
Purchase #7	$44.65	5.489%	$47.1008	$47.10	$47.10	$47.10
7 purchase totals =	$950.88		$1,031.6681	$1,031.67	$1,031.70	$1,031.60