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	$116.82	11.340%	$130.0674	$130.07	$130.05	$130.10
Purchase #2	$92.85	10.287%	$102.4015	$102.40	$102.40	$102.40
Purchase #3	$170.25	12.614%	$191.7253	$191.73	$191.75	$191.70
Purchase #4	$69.87	10.797%	$77.4139	$77.41	$77.40	$77.40
Purchase #5	$112.33	13.215%	$127.1744	$127.17	$127.15	$127.20
Purchase #6	$87.58	6.729%	$93.4733	$93.47	$93.45	$93.50
Purchase #7	$71.99	8.522%	$78.125	$78.13	$78.15	$78.10
7 purchase totals =	$721.69		$800.3808	$800.38	$800.35	$800.40