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	$12.39	9.593%	$13.5786	$13.58	$13.60	$13.60
Purchase #2	$133.31	11.471%	$148.602	$148.60	$148.60	$148.60
Purchase #3	$32.84	5.484%	$34.6409	$34.64	$34.65	$34.60
Purchase #4	$56.82	8.859%	$61.8537	$61.85	$61.85	$61.90
Purchase #5	$59.41	11.460%	$66.2184	$66.22	$66.20	$66.20
Purchase #6	$206.82	10.641%	$228.8277	$228.83	$228.85	$228.80
Purchase #7	$31.58	5.398%	$33.2847	$33.28	$33.30	$33.30
7 purchase totals =	$533.17		$587.0060	$587.00	$587.05	$587.00