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	$104.29	8.801%	$113.4686	$113.47	$113.45	$113.50
Purchase #2	$139.88	4.172%	$145.7158	$145.72	$145.70	$145.70
Purchase #3	$106.94	7.496%	$114.9562	$114.96	$114.95	$115.00
Purchase #4	$42.25	7.587%	$45.4555	$45.46	$45.45	$45.50
Purchase #5	$11.74	8.730%	$12.7649	$12.76	$12.75	$12.80
Purchase #6	$102.43	3.334%	$105.845	$105.85	$105.85	$105.80
Purchase #7	$9.85	11.121%	$10.9454	$10.95	$10.95	$10.90
7 purchase totals =	$517.38		$549.1514	$549.17	$549.10	$549.20