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	$102.80	3.518%	$106.4165	$106.42	$106.40	$106.40
Purchase #2	$87.79	5.810%	$92.8906	$92.89	$92.90	$92.90
Purchase #3	$123.94	8.718%	$134.7451	$134.75	$134.75	$134.70
Purchase #4	$85.98	11.523%	$95.8875	$95.89	$95.90	$95.90
Purchase #5	$217.93	12.705%	$245.618	$245.62	$245.60	$245.60
Purchase #6	$226.44	12.832%	$255.4968	$255.50	$255.50	$255.50
Purchase #7	$194.44	8.226%	$210.4346	$210.43	$210.45	$210.40
7 purchase totals =	$1,039.32		$1,141.4891	$1,141.50	$1,141.50	$1,141.40