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	$75.49	9.299%	$82.5098	$82.51	$82.50	$82.50
Purchase #2	$36.61	5.621%	$38.6678	$38.67	$38.65	$38.70
Purchase #3	$63.73	3.702%	$66.0893	$66.09	$66.10	$66.10
Purchase #4	$83.66	6.665%	$89.2359	$89.24	$89.25	$89.20
Purchase #5	$201.52	3.468%	$208.5087	$208.51	$208.50	$208.50
Purchase #6	$154.88	10.142%	$170.5879	$170.59	$170.60	$170.60
Purchase #7	$23.72	11.141%	$26.3626	$26.36	$26.35	$26.40
7 purchase totals =	$639.61		$681.9620	$681.97	$681.95	$682.00