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	$62.99	8.752%	$68.5029	$68.50	$68.50	$68.50
Purchase #2	$125.56	7.491%	$134.9657	$134.97	$134.95	$135.00
Purchase #3	$185.25	7.142%	$198.4806	$198.48	$198.50	$198.50
Purchase #4	$18.48	7.304%	$19.8298	$19.83	$19.85	$19.80
Purchase #5	$216.77	10.870%	$240.3329	$240.33	$240.35	$240.30
Purchase #6	$101.67	7.802%	$109.6023	$109.60	$109.60	$109.60
Purchase #7	$105.56	5.210%	$111.0597	$111.06	$111.05	$111.10
7 purchase totals =	$816.28		$882.7739	$882.77	$882.80	$882.80