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	$84.53	6.576%	$90.0887	$90.09	$90.10	$90.10
Purchase #2	$115.69	6.723%	$123.4678	$123.47	$123.45	$123.50
Purchase #3	$84.35	9.357%	$92.2426	$92.24	$92.25	$92.20
Purchase #4	$213.88	10.291%	$235.8904	$235.89	$235.90	$235.90
Purchase #5	$192.52	6.271%	$204.5929	$204.59	$204.60	$204.60
Purchase #6	$222.31	6.372%	$236.4756	$236.48	$236.50	$236.50
Purchase #7	$84.83	12.764%	$95.6577	$95.66	$95.65	$95.70
7 purchase totals =	$998.11		$1,078.4157	$1,078.42	$1,078.45	$1,078.50