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	$149.33	10.174%	$164.5228	$164.52	$164.50	$164.50
Purchase #2	$133.33	6.534%	$142.0418	$142.04	$142.05	$142.00
Purchase #3	$160.92	7.365%	$172.7718	$172.77	$172.75	$172.80
Purchase #4	$158.33	13.307%	$179.399	$179.40	$179.40	$179.40
Purchase #5	$69.62	9.189%	$76.0174	$76.02	$76.00	$76.00
Purchase #6	$7.77	12.148%	$8.7139	$8.71	$8.70	$8.70
Purchase #7	$246.59	3.491%	$255.1985	$255.20	$255.20	$255.20
7 purchase totals =	$925.89		$998.6652	$998.66	$998.60	$998.60