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	$16.46	13.389%	$18.6638	$18.66	$18.65	$18.70
Purchase #2	$132.43	9.522%	$145.04	$145.04	$145.05	$145.00
Purchase #3	$52.28	8.244%	$56.59	$56.59	$56.60	$56.60
Purchase #4	$71.89	6.134%	$76.2997	$76.30	$76.30	$76.30
Purchase #5	$82.61	8.238%	$89.4154	$89.42	$89.40	$89.40
Purchase #6	$116.52	5.606%	$123.0521	$123.05	$123.05	$123.10
Purchase #7	$86.90	10.826%	$96.3078	$96.31	$96.30	$96.30
7 purchase totals =	$559.09		$605.3688	$605.37	$605.35	$605.40