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	$90.63	4.396%	$94.6141	$94.61	$94.60	$94.60
Purchase #2	$233.37	9.583%	$255.7338	$255.73	$255.75	$255.70
Purchase #3	$196.35	10.265%	$216.5053	$216.51	$216.50	$216.50
Purchase #4	$233.77	7.724%	$251.8264	$251.83	$251.85	$251.80
Purchase #5	$58.27	4.581%	$60.9393	$60.94	$60.95	$60.90
Purchase #6	$50.86	13.300%	$57.6244	$57.62	$57.60	$57.60
Purchase #7	$47.27	9.639%	$51.8264	$51.83	$51.85	$51.80
7 purchase totals =	$910.52		$989.0697	$989.07	$989.10	$988.90