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	$32.87	5.328%	$34.6213	$34.62	$34.60	$34.60
Purchase #2	$180.58	10.487%	$199.5174	$199.52	$199.50	$199.50
Purchase #3	$73.61	4.285%	$76.7642	$76.76	$76.75	$76.80
Purchase #4	$50.55	4.568%	$52.8591	$52.86	$52.85	$52.90
Purchase #5	$33.76	6.255%	$35.8717	$35.87	$35.85	$35.90
Purchase #6	$156.94	5.119%	$164.9738	$164.97	$164.95	$165.00
Purchase #7	$75.91	9.244%	$82.9271	$82.93	$82.95	$82.90
7 purchase totals =	$604.22		$647.5346	$647.53	$647.45	$647.60