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	$143.58	11.149%	$159.5877	$159.59	$159.60	$159.60
Purchase #2	$21.39	12.394%	$24.0411	$24.04	$24.05	$24.00
Purchase #3	$134.90	4.612%	$141.1216	$141.12	$141.10	$141.10
Purchase #4	$103.99	8.758%	$113.0974	$113.10	$113.10	$113.10
Purchase #5	$59.27	3.140%	$61.1311	$61.13	$61.15	$61.10
Purchase #6	$98.30	6.687%	$104.8733	$104.87	$104.85	$104.90
Purchase #7	$161.53	11.196%	$179.6149	$179.61	$179.60	$179.60
7 purchase totals =	$722.96		$783.4671	$783.46	$783.45	$783.40