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	$90.70	11.557%	$101.1822	$101.18	$101.20	$101.20
Purchase #2	$130.90	13.372%	$148.4039	$148.40	$148.40	$148.40
Purchase #3	$49.27	3.806%	$51.1452	$51.15	$51.15	$51.10
Purchase #4	$88.41	13.500%	$100.3454	$100.35	$100.35	$100.30
Purchase #5	$131.72	8.307%	$142.662	$142.66	$142.65	$142.70
Purchase #6	$50.87	9.254%	$55.5775	$55.58	$55.60	$55.60
Purchase #7	$43.27	3.705%	$44.8732	$44.87	$44.85	$44.90
7 purchase totals =	$585.14		$644.1894	$644.19	$644.20	$644.20