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	$231.36	10.312%	$255.2178	$255.22	$255.20	$255.20
Purchase #2	$242.31	9.782%	$266.0128	$266.01	$266.00	$266.00
Purchase #3	$8.81	13.748%	$10.0212	$10.02	$10.00	$10.00
Purchase #4	$84.39	6.115%	$89.5504	$89.55	$89.55	$89.60
Purchase #5	$112.49	9.654%	$123.3498	$123.35	$123.35	$123.30
Purchase #6	$23.64	8.131%	$25.5622	$25.56	$25.55	$25.60
Purchase #7	$106.78	10.110%	$117.5755	$117.58	$117.60	$117.60
7 purchase totals =	$809.78		$887.2897	$887.29	$887.25	$887.30