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	$155.67	7.111%	$166.7397	$166.74	$166.75	$166.70
Purchase #2	$112.31	6.587%	$119.7079	$119.71	$119.70	$119.70
Purchase #3	$190.34	13.376%	$215.7999	$215.80	$215.80	$215.80
Purchase #4	$117.75	11.651%	$131.4691	$131.47	$131.45	$131.50
Purchase #5	$247.94	13.154%	$280.554	$280.55	$280.55	$280.60
Purchase #6	$6.49	8.624%	$7.0497	$7.05	$7.05	$7.00
Purchase #7	$82.91	4.171%	$86.3682	$86.37	$86.35	$86.40
7 purchase totals =	$913.41		$1,007.6885	$1,007.69	$1,007.65	$1,007.70