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	$22.86	7.695%	$24.6191	$24.62	$24.60	$24.60
Purchase #2	$24.47	12.746%	$27.5889	$27.59	$27.60	$27.60
Purchase #3	$104.32	11.767%	$116.5953	$116.60	$116.60	$116.60
Purchase #4	$137.37	9.196%	$150.0025	$150.00	$150.00	$150.00
Purchase #5	$71.83	8.415%	$77.8745	$77.87	$77.85	$77.90
Purchase #6	$55.51	5.467%	$58.5447	$58.54	$58.55	$58.50
Purchase #7	$117.51	7.737%	$126.6017	$126.60	$126.60	$126.60
7 purchase totals =	$533.87		$581.8267	$581.82	$581.80	$581.80