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	$14.37	10.381%	$15.8617	$15.86	$15.85	$15.90
Purchase #2	$99.77	4.140%	$103.9005	$103.90	$103.90	$103.90
Purchase #3	$152.53	7.269%	$163.6174	$163.62	$163.60	$163.60
Purchase #4	$187.59	11.795%	$209.7162	$209.72	$209.70	$209.70
Purchase #5	$145.90	8.327%	$158.0491	$158.05	$158.05	$158.00
Purchase #6	$16.94	11.509%	$18.8896	$18.89	$18.90	$18.90
Purchase #7	$43.38	5.737%	$45.8687	$45.87	$45.85	$45.90
7 purchase totals =	$660.48		$715.9032	$715.91	$715.85	$715.90