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	$82.62	8.766%	$89.8625	$89.86	$89.85	$89.90
Purchase #2	$157.25	12.565%	$177.0085	$177.01	$177.00	$177.00
Purchase #3	$59.60	10.417%	$65.8085	$65.81	$65.80	$65.80
Purchase #4	$192.59	13.434%	$218.4625	$218.46	$218.45	$218.50
Purchase #5	$10.42	4.226%	$10.8603	$10.86	$10.85	$10.90
Purchase #6	$7.85	11.447%	$8.7486	$8.75	$8.75	$8.70
Purchase #7	$88.32	9.845%	$97.0151	$97.02	$97.00	$97.00
7 purchase totals =	$598.65		$667.7660	$667.77	$667.70	$667.80