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	$82.65	8.205%	$89.4314	$89.43	$89.45	$89.40
Purchase #2	$122.78	9.686%	$134.6725	$134.67	$134.65	$134.70
Purchase #3	$51.85	4.336%	$54.0982	$54.10	$54.10	$54.10
Purchase #4	$186.64	13.867%	$212.5214	$212.52	$212.50	$212.50
Purchase #5	$213.91	9.610%	$234.4668	$234.47	$234.45	$234.50
Purchase #6	$116.48	3.731%	$120.8259	$120.83	$120.85	$120.80
Purchase #7	$20.64	4.507%	$21.5702	$21.57	$21.55	$21.60
7 purchase totals =	$794.95		$867.5864	$867.59	$867.55	$867.60