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	$44.47	13.481%	$50.465	$50.47	$50.45	$50.50
Purchase #2	$18.96	3.304%	$19.5864	$19.59	$19.60	$19.60
Purchase #3	$183.66	4.469%	$191.8678	$191.87	$191.85	$191.90
Purchase #4	$132.66	5.483%	$139.9337	$139.93	$139.95	$139.90
Purchase #5	$13.65	11.329%	$15.1964	$15.20	$15.20	$15.20
Purchase #6	$177.69	4.140%	$185.0464	$185.05	$185.05	$185.00
Purchase #7	$40.80	4.703%	$42.7188	$42.72	$42.70	$42.70
7 purchase totals =	$611.89		$644.8145	$644.83	$644.80	$644.80