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	$181.82	4.731%	$190.4219	$190.42	$190.40	$190.40
Purchase #2	$74.46	5.492%	$78.5493	$78.55	$78.55	$78.50
Purchase #3	$215.80	10.113%	$237.6239	$237.62	$237.60	$237.60
Purchase #4	$176.90	7.294%	$189.8031	$189.80	$189.80	$189.80
Purchase #5	$63.57	4.665%	$66.5355	$66.54	$66.55	$66.50
Purchase #6	$105.72	4.566%	$110.5472	$110.55	$110.55	$110.50
Purchase #7	$112.82	6.200%	$119.8148	$119.81	$119.80	$119.80
7 purchase totals =	$931.09		$993.2957	$993.29	$993.25	$993.10