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	$119.28	9.699%	$130.849	$130.85	$130.85	$130.80
Purchase #2	$216.98	10.169%	$239.0447	$239.04	$239.05	$239.00
Purchase #3	$35.67	13.552%	$40.504	$40.50	$40.50	$40.50
Purchase #4	$35.71	12.173%	$40.057	$40.06	$40.05	$40.10
Purchase #5	$123.70	12.855%	$139.6016	$139.60	$139.60	$139.60
Purchase #6	$215.53	11.734%	$240.8203	$240.82	$240.80	$240.80
Purchase #7	$82.29	5.315%	$86.6637	$86.66	$86.65	$86.70
7 purchase totals =	$829.16		$917.5403	$917.53	$917.50	$917.50