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	$134.70	7.419%	$144.6934	$144.69	$144.70	$144.70
Purchase #2	$87.64	3.370%	$90.5935	$90.59	$90.60	$90.60
Purchase #3	$55.84	10.209%	$61.5407	$61.54	$61.55	$61.50
Purchase #4	$140.98	13.412%	$159.8882	$159.89	$159.90	$159.90
Purchase #5	$241.88	13.866%	$275.4191	$275.42	$275.40	$275.40
Purchase #6	$35.77	13.131%	$40.467	$40.47	$40.45	$40.50
Purchase #7	$190.25	10.828%	$210.8503	$210.85	$210.85	$210.90
7 purchase totals =	$887.06		$983.4522	$983.45	$983.45	$983.50