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	$72.28	8.605%	$78.4997	$78.50	$78.50	$78.50
Purchase #2	$23.50	10.236%	$25.9055	$25.91	$25.90	$25.90
Purchase #3	$106.29	12.682%	$119.7697	$119.77	$119.75	$119.80
Purchase #4	$86.66	7.146%	$92.8527	$92.85	$92.85	$92.90
Purchase #5	$5.73	12.373%	$6.439	$6.44	$6.45	$6.40
Purchase #6	$237.55	3.509%	$245.8856	$245.89	$245.90	$245.90
Purchase #7	$54.29	9.571%	$59.4861	$59.49	$59.50	$59.50
7 purchase totals =	$586.30		$628.8383	$628.85	$628.85	$628.90