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	$12.43	8.327%	$13.465	$13.47	$13.45	$13.50
Purchase #2	$153.33	12.279%	$172.1574	$172.16	$172.15	$172.20
Purchase #3	$12.54	3.250%	$12.9476	$12.95	$12.95	$12.90
Purchase #4	$46.80	11.437%	$52.1525	$52.15	$52.15	$52.20
Purchase #5	$12.41	10.538%	$13.7178	$13.72	$13.70	$13.70
Purchase #6	$13.29	5.687%	$14.0458	$14.05	$14.05	$14.00
Purchase #7	$222.38	3.213%	$229.5251	$229.53	$229.55	$229.50
7 purchase totals =	$473.18		$508.0112	$508.03	$508.00	$508.00