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	$99.63	13.223%	$112.8041	$112.80	$112.80	$112.80
Purchase #2	$226.88	12.606%	$255.4805	$255.48	$255.50	$255.50
Purchase #3	$205.88	10.508%	$227.5139	$227.51	$227.50	$227.50
Purchase #4	$175.91	8.161%	$190.266	$190.27	$190.25	$190.30
Purchase #5	$215.74	9.845%	$236.9796	$236.98	$237.00	$237.00
Purchase #6	$226.54	6.275%	$240.7554	$240.76	$240.75	$240.80
Purchase #7	$117.45	12.287%	$131.8811	$131.88	$131.90	$131.90
7 purchase totals =	$1,268.03		$1,395.6806	$1,395.68	$1,395.70	$1,395.80