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	$29.57	11.310%	$32.9144	$32.91	$32.90	$32.90
Purchase #2	$36.26	13.143%	$41.0257	$41.03	$41.05	$41.00
Purchase #3	$207.86	3.176%	$214.4616	$214.46	$214.45	$214.50
Purchase #4	$16.34	12.170%	$18.3286	$18.33	$18.35	$18.30
Purchase #5	$164.37	8.390%	$178.1606	$178.16	$178.15	$178.20
Purchase #6	$151.49	8.666%	$164.6181	$164.62	$164.60	$164.60
Purchase #7	$111.99	10.433%	$123.6739	$123.67	$123.65	$123.70
7 purchase totals =	$717.88		$773.1829	$773.18	$773.15	$773.20