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	$184.87	11.172%	$205.5237	$205.52	$205.50	$205.50
Purchase #2	$130.47	10.593%	$144.2907	$144.29	$144.30	$144.30
Purchase #3	$120.77	3.170%	$124.5984	$124.60	$124.60	$124.60
Purchase #4	$105.56	8.847%	$114.8989	$114.90	$114.90	$114.90
Purchase #5	$126.70	13.214%	$143.4421	$143.44	$143.45	$143.40
Purchase #6	$105.98	12.779%	$119.5232	$119.52	$119.50	$119.50
Purchase #7	$16.35	10.481%	$18.0636	$18.06	$18.05	$18.10
7 purchase totals =	$790.70		$870.3406	$870.33	$870.30	$870.30