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	$18.78	3.493%	$19.436	$19.44	$19.45	$19.40
Purchase #2	$187.35	12.368%	$210.5214	$210.52	$210.50	$210.50
Purchase #3	$241.73	6.859%	$258.3103	$258.31	$258.30	$258.30
Purchase #4	$160.48	9.758%	$176.1396	$176.14	$176.15	$176.10
Purchase #5	$56.96	4.508%	$59.5278	$59.53	$59.55	$59.50
Purchase #6	$93.67	3.574%	$97.0178	$97.02	$97.00	$97.00
Purchase #7	$16.77	12.241%	$18.8228	$18.82	$18.80	$18.80
7 purchase totals =	$775.74		$839.7757	$839.78	$839.75	$839.60