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	$89.78	10.150%	$98.8927	$98.89	$98.90	$98.90
Purchase #2	$204.58	5.554%	$215.9424	$215.94	$215.95	$215.90
Purchase #3	$208.65	4.241%	$217.4988	$217.50	$217.50	$217.50
Purchase #4	$206.62	10.376%	$228.0589	$228.06	$228.05	$228.10
Purchase #5	$237.71	7.304%	$255.0723	$255.07	$255.05	$255.10
Purchase #6	$33.25	5.303%	$35.0132	$35.01	$35.00	$35.00
Purchase #7	$246.89	10.328%	$272.3888	$272.39	$272.40	$272.40
7 purchase totals =	$1,227.48		$1,322.8671	$1,322.86	$1,322.85	$1,322.90