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	$24.32	5.640%	$25.6916	$25.69	$25.70	$25.70
Purchase #2	$65.44	10.730%	$72.4617	$72.46	$72.45	$72.50
Purchase #3	$232.61	10.835%	$257.8133	$257.81	$257.80	$257.80
Purchase #4	$146.77	3.612%	$152.0713	$152.07	$152.05	$152.10
Purchase #5	$172.38	11.215%	$191.7124	$191.71	$191.70	$191.70
Purchase #6	$19.76	10.335%	$21.8022	$21.80	$21.80	$21.80
Purchase #7	$131.43	9.276%	$143.6214	$143.62	$143.60	$143.60
7 purchase totals =	$792.71		$865.1739	$865.16	$865.10	$865.20