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	$18.94	3.771%	$19.6542	$19.65	$19.65	$19.70
Purchase #2	$119.81	6.517%	$127.618	$127.62	$127.60	$127.60
Purchase #3	$98.28	10.373%	$108.4746	$108.47	$108.45	$108.50
Purchase #4	$237.59	11.863%	$265.7753	$265.78	$265.80	$265.80
Purchase #5	$213.64	3.684%	$221.5105	$221.51	$221.50	$221.50
Purchase #6	$60.51	11.834%	$67.6708	$67.67	$67.65	$67.70
Purchase #7	$119.61	8.807%	$130.1441	$130.14	$130.15	$130.10
7 purchase totals =	$868.38		$940.8475	$940.84	$940.80	$940.90