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	$76.76	11.385%	$85.4991	$85.50	$85.50	$85.50
Purchase #2	$64.38	8.808%	$70.0506	$70.05	$70.05	$70.10
Purchase #3	$59.97	4.485%	$62.6597	$62.66	$62.65	$62.70
Purchase #4	$113.49	8.847%	$123.5305	$123.53	$123.55	$123.50
Purchase #5	$184.27	11.402%	$205.2805	$205.28	$205.30	$205.30
Purchase #6	$169.30	5.223%	$178.1425	$178.14	$178.15	$178.10
Purchase #7	$92.85	12.524%	$104.4785	$104.48	$104.50	$104.50
7 purchase totals =	$761.02		$829.6414	$829.64	$829.70	$829.70