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	$35.31	9.387%	$38.6245	$38.62	$38.60	$38.60
Purchase #2	$55.48	13.106%	$62.7512	$62.75	$62.75	$62.80
Purchase #3	$215.81	10.716%	$238.9362	$238.94	$238.95	$238.90
Purchase #4	$141.90	7.720%	$152.8547	$152.85	$152.85	$152.90
Purchase #5	$122.99	9.673%	$134.8868	$134.89	$134.90	$134.90
Purchase #6	$134.88	11.396%	$150.2509	$150.25	$150.25	$150.30
Purchase #7	$182.66	13.250%	$206.8625	$206.86	$206.85	$206.90
7 purchase totals =	$889.03		$985.1668	$985.16	$985.15	$985.30