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	$239.68	6.844%	$256.0837	$256.08	$256.10	$256.10
Purchase #2	$78.60	6.107%	$83.4001	$83.40	$83.40	$83.40
Purchase #3	$72.52	12.509%	$81.5915	$81.59	$81.60	$81.60
Purchase #4	$25.59	9.108%	$27.9207	$27.92	$27.90	$27.90
Purchase #5	$39.46	5.165%	$41.4981	$41.50	$41.50	$41.50
Purchase #6	$196.89	13.351%	$223.1768	$223.18	$223.20	$223.20
Purchase #7	$232.79	6.611%	$248.1797	$248.18	$248.20	$248.20
7 purchase totals =	$885.53		$961.8506	$961.85	$961.90	$961.90