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	$9.47	5.252%	$9.9674	$9.97	$9.95	$10.00
Purchase #2	$186.81	6.850%	$199.6065	$199.61	$199.60	$199.60
Purchase #3	$162.53	3.282%	$167.8642	$167.86	$167.85	$167.90
Purchase #4	$102.42	11.243%	$113.9351	$113.94	$113.95	$113.90
Purchase #5	$122.46	10.190%	$134.9387	$134.94	$134.95	$134.90
Purchase #6	$71.41	10.483%	$78.8959	$78.90	$78.90	$78.90
Purchase #7	$237.27	7.721%	$255.5896	$255.59	$255.60	$255.60
7 purchase totals =	$892.37		$960.7974	$960.81	$960.80	$960.80