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	$83.83	7.802%	$90.3704	$90.37	$90.35	$90.40
Purchase #2	$84.89	10.745%	$94.0114	$94.01	$94.00	$94.00
Purchase #3	$37.40	8.579%	$40.6085	$40.61	$40.60	$40.60
Purchase #4	$157.39	5.696%	$166.3549	$166.35	$166.35	$166.40
Purchase #5	$143.52	10.766%	$158.9714	$158.97	$158.95	$159.00
Purchase #6	$248.47	11.856%	$277.9286	$277.93	$277.95	$277.90
Purchase #7	$84.89	8.660%	$92.2415	$92.24	$92.25	$92.20
7 purchase totals =	$840.39		$920.4867	$920.48	$920.45	$920.50