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	$54.63	12.509%	$61.4637	$61.46	$61.45	$61.50
Purchase #2	$86.32	11.115%	$95.9145	$95.91	$95.90	$95.90
Purchase #3	$41.35	13.868%	$47.0844	$47.08	$47.10	$47.10
Purchase #4	$31.46	12.377%	$35.3538	$35.35	$35.35	$35.40
Purchase #5	$113.36	8.508%	$123.0047	$123.00	$123.00	$123.00
Purchase #6	$157.70	13.782%	$179.4342	$179.43	$179.45	$179.40
Purchase #7	$89.70	8.810%	$97.6026	$97.60	$97.60	$97.60
7 purchase totals =	$574.52		$639.8579	$639.83	$639.85	$639.90