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	$123.39	6.538%	$131.4572	$131.46	$131.45	$131.50
Purchase #2	$22.57	7.836%	$24.3386	$24.34	$24.35	$24.30
Purchase #3	$198.46	12.271%	$222.813	$222.81	$222.80	$222.80
Purchase #4	$250.68	11.699%	$280.0071	$280.01	$280.00	$280.00
Purchase #5	$239.55	5.359%	$252.3875	$252.39	$252.40	$252.40
Purchase #6	$188.25	13.841%	$214.3057	$214.31	$214.30	$214.30
Purchase #7	$26.29	4.404%	$27.4478	$27.45	$27.45	$27.40
7 purchase totals =	$1,049.19		$1,152.7569	$1,152.77	$1,152.75	$1,152.70