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	$10.64	11.552%	$11.8691	$11.87	$11.85	$11.90
Purchase #2	$184.48	3.319%	$190.6029	$190.60	$190.60	$190.60
Purchase #3	$245.98	12.510%	$276.7521	$276.75	$276.75	$276.80
Purchase #4	$157.81	3.218%	$162.8883	$162.89	$162.90	$162.90
Purchase #5	$146.63	7.760%	$158.0085	$158.01	$158.00	$158.00
Purchase #6	$150.96	3.667%	$156.4957	$156.50	$156.50	$156.50
Purchase #7	$153.25	9.655%	$168.0463	$168.05	$168.05	$168.00
7 purchase totals =	$1,049.75		$1,124.6629	$1,124.67	$1,124.65	$1,124.70