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	$6.72	13.249%	$7.6103	$7.61	$7.60	$7.60
Purchase #2	$131.38	5.218%	$138.2354	$138.24	$138.25	$138.20
Purchase #3	$201.67	6.854%	$215.4925	$215.49	$215.50	$215.50
Purchase #4	$222.72	10.249%	$245.5466	$245.55	$245.55	$245.50
Purchase #5	$76.81	7.808%	$82.8073	$82.81	$82.80	$82.80
Purchase #6	$102.51	3.492%	$106.0896	$106.09	$106.10	$106.10
Purchase #7	$172.82	9.137%	$188.6106	$188.61	$188.60	$188.60
7 purchase totals =	$914.63		$984.3923	$984.40	$984.40	$984.30