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	$155.78	8.352%	$168.7907	$168.79	$168.80	$168.80
Purchase #2	$131.45	11.657%	$146.7731	$146.77	$146.75	$146.80
Purchase #3	$83.93	11.603%	$93.6684	$93.67	$93.65	$93.70
Purchase #4	$219.28	6.834%	$234.2656	$234.27	$234.25	$234.30
Purchase #5	$153.81	5.714%	$162.5987	$162.60	$162.60	$162.60
Purchase #6	$90.87	13.628%	$103.2538	$103.25	$103.25	$103.30
Purchase #7	$71.73	9.369%	$78.4504	$78.45	$78.45	$78.50
7 purchase totals =	$906.85		$987.8007	$987.80	$987.75	$988.00