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	$47.32	10.866%	$52.4618	$52.46	$52.45	$52.50
Purchase #2	$136.96	4.845%	$143.5957	$143.60	$143.60	$143.60
Purchase #3	$52.29	13.792%	$59.5018	$59.50	$59.50	$59.50
Purchase #4	$63.79	12.623%	$71.8422	$71.84	$71.85	$71.80
Purchase #5	$50.90	13.308%	$57.6738	$57.67	$57.65	$57.70
Purchase #6	$9.63	7.311%	$10.334	$10.33	$10.35	$10.30
Purchase #7	$196.86	9.340%	$215.2467	$215.25	$215.25	$215.20
7 purchase totals =	$557.75		$610.6560	$610.65	$610.65	$610.60