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	$90.41	9.554%	$99.0478	$99.05	$99.05	$99.00
Purchase #2	$52.93	12.717%	$59.6611	$59.66	$59.65	$59.70
Purchase #3	$42.82	11.510%	$47.7486	$47.75	$47.75	$47.70
Purchase #4	$201.79	13.177%	$228.3799	$228.38	$228.40	$228.40
Purchase #5	$100.67	13.597%	$114.3581	$114.36	$114.35	$114.40
Purchase #6	$234.38	5.351%	$246.9217	$246.92	$246.90	$246.90
Purchase #7	$63.38	7.160%	$67.918	$67.92	$67.90	$67.90
7 purchase totals =	$786.38		$864.0352	$864.04	$864.00	$864.00