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	$9.68	7.673%	$10.4227	$10.42	$10.40	$10.40
Purchase #2	$34.79	12.345%	$39.0848	$39.08	$39.10	$39.10
Purchase #3	$95.96	4.473%	$100.2523	$100.25	$100.25	$100.30
Purchase #4	$44.43	9.410%	$48.6109	$48.61	$48.60	$48.60
Purchase #5	$32.30	8.445%	$35.0277	$35.03	$35.05	$35.00
Purchase #6	$38.93	4.242%	$40.5814	$40.58	$40.60	$40.60
Purchase #7	$80.35	3.348%	$83.0401	$83.04	$83.05	$83.00
7 purchase totals =	$336.44		$357.0199	$357.01	$357.05	$357.00