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	$142.47	6.154%	$151.2376	$151.24	$151.25	$151.20
Purchase #2	$50.50	12.685%	$56.9059	$56.91	$56.90	$56.90
Purchase #3	$117.58	5.370%	$123.894	$123.89	$123.90	$123.90
Purchase #4	$138.51	11.189%	$154.0079	$154.01	$154.00	$154.00
Purchase #5	$136.26	4.517%	$142.4149	$142.41	$142.40	$142.40
Purchase #6	$28.52	3.678%	$29.569	$29.57	$29.55	$29.60
Purchase #7	$49.56	4.436%	$51.7585	$51.76	$51.75	$51.80
7 purchase totals =	$663.40		$709.7878	$709.79	$709.75	$709.80