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	$240.90	3.391%	$249.0689	$249.07	$249.05	$249.10
Purchase #2	$7.94	7.208%	$8.5123	$8.51	$8.50	$8.50
Purchase #3	$66.45	9.716%	$72.9063	$72.91	$72.90	$72.90
Purchase #4	$34.82	9.381%	$38.0865	$38.09	$38.10	$38.10
Purchase #5	$209.57	11.405%	$233.4715	$233.47	$233.45	$233.50
Purchase #6	$99.92	5.691%	$105.6064	$105.61	$105.60	$105.60
Purchase #7	$239.32	10.377%	$264.1542	$264.15	$264.15	$264.20
7 purchase totals =	$898.92		$971.8061	$971.81	$971.75	$971.90