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	$10.44	3.450%	$10.8002	$10.80	$10.80	$10.80
Purchase #2	$196.54	10.330%	$216.8426	$216.84	$216.85	$216.80
Purchase #3	$181.87	10.189%	$200.4007	$200.40	$200.40	$200.40
Purchase #4	$222.49	4.769%	$233.1005	$233.10	$233.10	$233.10
Purchase #5	$111.75	8.550%	$121.3046	$121.30	$121.30	$121.30
Purchase #6	$112.47	9.627%	$123.2975	$123.30	$123.30	$123.30
Purchase #7	$65.78	11.858%	$73.5802	$73.58	$73.60	$73.60
7 purchase totals =	$901.34		$979.3263	$979.32	$979.35	$979.30