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	$12.83	6.167%	$13.6212	$13.62	$13.60	$13.60
Purchase #2	$242.25	13.329%	$274.5395	$274.54	$274.55	$274.50
Purchase #3	$96.78	12.388%	$108.7691	$108.77	$108.75	$108.80
Purchase #4	$125.96	4.866%	$132.0892	$132.09	$132.10	$132.10
Purchase #5	$34.95	6.488%	$37.2176	$37.22	$37.20	$37.20
Purchase #6	$238.88	10.741%	$264.5381	$264.54	$264.55	$264.50
Purchase #7	$12.59	5.221%	$13.2473	$13.25	$13.25	$13.20
7 purchase totals =	$764.24		$844.0220	$844.03	$844.00	$843.90