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	$137.98	13.516%	$156.6294	$156.63	$156.65	$156.60
Purchase #2	$137.87	6.478%	$146.8012	$146.80	$146.80	$146.80
Purchase #3	$153.50	12.484%	$172.6629	$172.66	$172.65	$172.70
Purchase #4	$43.61	11.392%	$48.5781	$48.58	$48.60	$48.60
Purchase #5	$123.99	8.541%	$134.58	$134.58	$134.60	$134.60
Purchase #6	$130.52	9.283%	$142.6362	$142.64	$142.65	$142.60
Purchase #7	$92.80	3.339%	$95.8986	$95.90	$95.90	$95.90
7 purchase totals =	$820.27		$897.7864	$897.79	$897.85	$897.80