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	$67.70	3.413%	$70.0106	$70.01	$70.00	$70.00
Purchase #2	$69.44	13.519%	$78.8276	$78.83	$78.85	$78.80
Purchase #3	$194.43	10.623%	$215.0843	$215.08	$215.10	$215.10
Purchase #4	$62.75	12.509%	$70.5994	$70.60	$70.60	$70.60
Purchase #5	$116.56	9.493%	$127.625	$127.63	$127.65	$127.60
Purchase #6	$214.89	7.779%	$231.6063	$231.61	$231.60	$231.60
Purchase #7	$101.73	9.611%	$111.5073	$111.51	$111.50	$111.50
7 purchase totals =	$827.50		$905.2605	$905.27	$905.30	$905.20