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	$246.65	13.598%	$280.1895	$280.19	$280.20	$280.20
Purchase #2	$97.67	6.274%	$103.7978	$103.80	$103.80	$103.80
Purchase #3	$124.51	9.699%	$136.5862	$136.59	$136.60	$136.60
Purchase #4	$68.49	4.677%	$71.6933	$71.69	$71.70	$71.70
Purchase #5	$185.92	5.513%	$196.1698	$196.17	$196.15	$196.20
Purchase #6	$120.92	11.225%	$134.4933	$134.49	$134.50	$134.50
Purchase #7	$103.87	4.715%	$108.7675	$108.77	$108.75	$108.80
7 purchase totals =	$948.03		$1,031.6974	$1,031.70	$1,031.70	$1,031.80