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	$238.40	8.712%	$259.1694	$259.17	$259.15	$259.20
Purchase #2	$98.64	7.142%	$105.6849	$105.68	$105.70	$105.70
Purchase #3	$109.64	12.832%	$123.709	$123.71	$123.70	$123.70
Purchase #4	$174.25	8.821%	$189.6206	$189.62	$189.60	$189.60
Purchase #5	$237.35	7.536%	$255.2367	$255.24	$255.25	$255.20
Purchase #6	$219.86	12.579%	$247.5162	$247.52	$247.50	$247.50
Purchase #7	$63.32	5.666%	$66.9077	$66.91	$66.90	$66.90
7 purchase totals =	$1,141.46		$1,247.8445	$1,247.85	$1,247.80	$1,247.80