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	$158.71	7.379%	$170.4212	$170.42	$170.40	$170.40
Purchase #2	$228.94	11.765%	$255.8748	$255.87	$255.85	$255.90
Purchase #3	$212.57	8.203%	$230.0071	$230.01	$230.00	$230.00
Purchase #4	$131.46	12.150%	$147.4324	$147.43	$147.45	$147.40
Purchase #5	$83.32	9.329%	$91.0929	$91.09	$91.10	$91.10
Purchase #6	$53.71	10.515%	$59.3576	$59.36	$59.35	$59.40
Purchase #7	$117.38	3.689%	$121.7101	$121.71	$121.70	$121.70
7 purchase totals =	$986.09		$1,075.8961	$1,075.89	$1,075.85	$1,075.90