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	$38.71	10.715%	$42.8578	$42.86	$42.85	$42.90
Purchase #2	$138.40	11.567%	$154.4087	$154.41	$154.40	$154.40
Purchase #3	$35.48	4.529%	$37.0869	$37.09	$37.10	$37.10
Purchase #4	$48.55	11.182%	$53.9789	$53.98	$54.00	$54.00
Purchase #5	$135.48	5.165%	$142.4775	$142.48	$142.50	$142.50
Purchase #6	$108.35	12.652%	$122.0584	$122.06	$122.05	$122.10
Purchase #7	$245.39	3.486%	$253.9443	$253.94	$253.95	$253.90
7 purchase totals =	$750.36		$806.8125	$806.82	$806.85	$806.90