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	$52.93	8.582%	$57.4725	$57.47	$57.45	$57.50
Purchase #2	$86.29	4.156%	$89.8762	$89.88	$89.90	$89.90
Purchase #3	$72.85	10.622%	$80.5881	$80.59	$80.60	$80.60
Purchase #4	$6.40	6.621%	$6.8237	$6.82	$6.80	$6.80
Purchase #5	$179.87	4.493%	$187.9516	$187.95	$187.95	$188.00
Purchase #6	$205.34	5.171%	$215.9581	$215.96	$215.95	$216.00
Purchase #7	$165.57	10.742%	$183.3555	$183.36	$183.35	$183.40
7 purchase totals =	$769.25		$822.0257	$822.03	$822.00	$822.20