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	$88.83	3.340%	$91.7969	$91.80	$91.80	$91.80
Purchase #2	$224.60	13.705%	$255.3814	$255.38	$255.40	$255.40
Purchase #3	$56.58	7.129%	$60.6136	$60.61	$60.60	$60.60
Purchase #4	$78.62	13.309%	$89.0835	$89.08	$89.10	$89.10
Purchase #5	$215.65	10.574%	$238.4528	$238.45	$238.45	$238.50
Purchase #6	$146.89	8.835%	$159.8677	$159.87	$159.85	$159.90
Purchase #7	$18.68	5.287%	$19.6676	$19.67	$19.65	$19.70
7 purchase totals =	$829.85		$914.8635	$914.86	$914.85	$915.00