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	$221.54	12.528%	$249.2945	$249.29	$249.30	$249.30
Purchase #2	$108.45	10.378%	$119.7049	$119.70	$119.70	$119.70
Purchase #3	$123.39	4.429%	$128.8549	$128.85	$128.85	$128.90
Purchase #4	$215.62	13.427%	$244.5713	$244.57	$244.55	$244.60
Purchase #5	$21.30	9.164%	$23.2519	$23.25	$23.25	$23.30
Purchase #6	$64.43	5.342%	$67.8719	$67.87	$67.85	$67.90
Purchase #7	$116.65	12.828%	$131.6139	$131.61	$131.60	$131.60
7 purchase totals =	$871.38		$965.1633	$965.14	$965.10	$965.30