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	$124.94	11.252%	$138.9982	$139.00	$139.00	$139.00
Purchase #2	$18.99	8.698%	$20.6418	$20.64	$20.65	$20.60
Purchase #3	$108.89	13.123%	$123.1796	$123.18	$123.20	$123.20
Purchase #4	$25.62	6.364%	$27.2505	$27.25	$27.25	$27.30
Purchase #5	$142.88	11.319%	$159.0526	$159.05	$159.05	$159.10
Purchase #6	$100.51	9.794%	$110.3539	$110.35	$110.35	$110.40
Purchase #7	$104.29	4.452%	$108.933	$108.93	$108.95	$108.90
7 purchase totals =	$626.12		$688.4096	$688.40	$688.45	$688.50