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	$29.33	6.246%	$31.162	$31.16	$31.15	$31.20
Purchase #2	$108.65	3.626%	$112.5896	$112.59	$112.60	$112.60
Purchase #3	$131.87	10.313%	$145.4698	$145.47	$145.45	$145.50
Purchase #4	$92.42	13.305%	$104.7165	$104.72	$104.70	$104.70
Purchase #5	$219.26	6.386%	$233.2619	$233.26	$233.25	$233.30
Purchase #6	$161.89	13.198%	$183.2562	$183.26	$183.25	$183.30
Purchase #7	$113.41	5.723%	$119.9005	$119.90	$119.90	$119.90
7 purchase totals =	$856.83		$930.3565	$930.36	$930.30	$930.50