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	$59.78	9.742%	$65.6038	$65.60	$65.60	$65.60
Purchase #2	$28.65	8.224%	$31.0062	$31.01	$31.00	$31.00
Purchase #3	$138.47	3.527%	$143.3538	$143.35	$143.35	$143.40
Purchase #4	$74.31	11.136%	$82.5852	$82.59	$82.60	$82.60
Purchase #5	$92.53	4.263%	$96.4746	$96.47	$96.45	$96.50
Purchase #6	$171.77	9.618%	$188.2908	$188.29	$188.30	$188.30
Purchase #7	$7.83	9.213%	$8.5514	$8.55	$8.55	$8.60
7 purchase totals =	$573.34		$615.8658	$615.86	$615.85	$616.00