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	$144.57	13.509%	$164.1	$164.10	$164.10	$164.10
Purchase #2	$122.89	4.460%	$128.3709	$128.37	$128.35	$128.40
Purchase #3	$241.70	5.559%	$255.1361	$255.14	$255.15	$255.10
Purchase #4	$177.59	7.629%	$191.1383	$191.14	$191.15	$191.10
Purchase #5	$159.71	7.178%	$171.174	$171.17	$171.15	$171.20
Purchase #6	$34.75	7.368%	$37.3104	$37.31	$37.30	$37.30
Purchase #7	$117.25	9.741%	$128.6713	$128.67	$128.65	$128.70
7 purchase totals =	$998.46		$1,075.9010	$1,075.90	$1,075.85	$1,075.90