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	$91.54	13.744%	$104.1213	$104.12	$104.10	$104.10
Purchase #2	$195.30	9.364%	$213.5879	$213.59	$213.60	$213.60
Purchase #3	$125.30	5.746%	$132.4997	$132.50	$132.50	$132.50
Purchase #4	$82.34	10.851%	$91.2747	$91.27	$91.25	$91.30
Purchase #5	$37.26	4.189%	$38.8208	$38.82	$38.80	$38.80
Purchase #6	$143.63	8.806%	$156.2781	$156.28	$156.30	$156.30
Purchase #7	$126.43	4.745%	$132.4291	$132.43	$132.45	$132.40
7 purchase totals =	$801.80		$869.0116	$869.01	$869.00	$869.00