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	$103.38	12.786%	$116.5982	$116.60	$116.60	$116.60
Purchase #2	$112.63	10.755%	$124.7434	$124.74	$124.75	$124.70
Purchase #3	$59.57	3.255%	$61.509	$61.51	$61.50	$61.50
Purchase #4	$208.97	11.442%	$232.8803	$232.88	$232.90	$232.90
Purchase #5	$64.87	12.236%	$72.8075	$72.81	$72.80	$72.80
Purchase #6	$196.58	6.720%	$209.7902	$209.79	$209.80	$209.80
Purchase #7	$157.64	9.536%	$172.6726	$172.67	$172.65	$172.70
7 purchase totals =	$903.64		$991.0012	$991.00	$991.00	$991.00