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	$159.78	10.684%	$176.8509	$176.85	$176.85	$176.90
Purchase #2	$222.55	7.456%	$239.1433	$239.14	$239.15	$239.10
Purchase #3	$125.31	11.261%	$139.4212	$139.42	$139.40	$139.40
Purchase #4	$57.54	5.203%	$60.5338	$60.53	$60.55	$60.50
Purchase #5	$238.94	7.742%	$257.4387	$257.44	$257.45	$257.40
Purchase #6	$54.90	7.558%	$59.0493	$59.05	$59.05	$59.00
Purchase #7	$61.87	13.534%	$70.2435	$70.24	$70.25	$70.20
7 purchase totals =	$920.89		$1,002.6807	$1,002.67	$1,002.70	$1,002.50