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	$238.79	13.362%	$270.6971	$270.70	$270.70	$270.70
Purchase #2	$212.92	5.676%	$225.0053	$225.01	$225.00	$225.00
Purchase #3	$127.99	9.308%	$139.9033	$139.90	$139.90	$139.90
Purchase #4	$195.89	4.781%	$205.2555	$205.26	$205.25	$205.30
Purchase #5	$114.75	11.235%	$127.6422	$127.64	$127.65	$127.60
Purchase #6	$116.38	12.863%	$131.35	$131.35	$131.35	$131.40
Purchase #7	$17.31	8.666%	$18.8101	$18.81	$18.80	$18.80
7 purchase totals =	$1,024.03		$1,118.6635	$1,118.67	$1,118.65	$1,118.70