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	$32.31	10.586%	$35.7303	$35.73	$35.75	$35.70
Purchase #2	$208.99	8.271%	$226.2756	$226.28	$226.30	$226.30
Purchase #3	$152.85	3.682%	$158.4779	$158.48	$158.50	$158.50
Purchase #4	$9.64	8.555%	$10.4647	$10.46	$10.45	$10.50
Purchase #5	$70.64	10.471%	$78.0367	$78.04	$78.05	$78.00
Purchase #6	$22.38	12.725%	$25.2279	$25.23	$25.25	$25.20
Purchase #7	$34.81	7.375%	$37.3772	$37.38	$37.40	$37.40
7 purchase totals =	$531.62		$571.5903	$571.60	$571.70	$571.60