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	$237.63	4.846%	$249.1455	$249.15	$249.15	$249.10
Purchase #2	$13.87	4.538%	$14.4994	$14.50	$14.50	$14.50
Purchase #3	$112.37	9.798%	$123.38	$123.38	$123.40	$123.40
Purchase #4	$248.65	13.760%	$282.8642	$282.86	$282.85	$282.90
Purchase #5	$123.96	12.174%	$139.0509	$139.05	$139.05	$139.10
Purchase #6	$87.55	13.706%	$99.5496	$99.55	$99.55	$99.50
Purchase #7	$23.26	6.468%	$24.7645	$24.76	$24.75	$24.80
7 purchase totals =	$847.29		$933.2541	$933.25	$933.25	$933.30