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	$249.34	12.509%	$280.5299	$280.53	$280.55	$280.50
Purchase #2	$227.32	4.456%	$237.4494	$237.45	$237.45	$237.40
Purchase #3	$231.46	13.226%	$262.0729	$262.07	$262.05	$262.10
Purchase #4	$152.33	6.296%	$161.9207	$161.92	$161.90	$161.90
Purchase #5	$71.94	9.109%	$78.493	$78.49	$78.50	$78.50
Purchase #6	$205.37	9.567%	$225.0177	$225.02	$225.00	$225.00
Purchase #7	$229.64	10.265%	$253.2125	$253.21	$253.20	$253.20
7 purchase totals =	$1,367.40		$1,498.6961	$1,498.69	$1,498.65	$1,498.60