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	$65.71	7.786%	$70.8262	$70.83	$70.85	$70.80
Purchase #2	$249.46	10.601%	$275.9053	$275.91	$275.90	$275.90
Purchase #3	$13.60	10.267%	$14.9963	$15.00	$15.00	$15.00
Purchase #4	$39.70	9.478%	$43.4628	$43.46	$43.45	$43.50
Purchase #5	$57.78	8.347%	$62.6029	$62.60	$62.60	$62.60
Purchase #6	$24.67	5.718%	$26.0806	$26.08	$26.10	$26.10
Purchase #7	$43.45	3.520%	$44.9794	$44.98	$45.00	$45.00
7 purchase totals =	$494.37		$538.8535	$538.86	$538.90	$538.90