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	$35.62	12.325%	$40.0102	$40.01	$40.00	$40.00
Purchase #2	$205.80	8.459%	$223.2086	$223.21	$223.20	$223.20
Purchase #3	$76.69	8.554%	$83.2501	$83.25	$83.25	$83.30
Purchase #4	$126.35	6.480%	$134.5375	$134.54	$134.55	$134.50
Purchase #5	$42.39	9.391%	$46.3708	$46.37	$46.35	$46.40
Purchase #6	$95.32	9.602%	$104.4726	$104.47	$104.45	$104.50
Purchase #7	$87.76	5.514%	$92.5991	$92.60	$92.60	$92.60
7 purchase totals =	$669.93		$724.4489	$724.45	$724.40	$724.50