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	$28.26	9.253%	$30.8749	$30.87	$30.85	$30.90
Purchase #2	$130.85	12.179%	$146.7862	$146.79	$146.80	$146.80
Purchase #3	$130.65	8.149%	$141.2967	$141.30	$141.30	$141.30
Purchase #4	$246.43	13.662%	$280.0973	$280.10	$280.10	$280.10
Purchase #5	$156.77	13.836%	$178.4607	$178.46	$178.45	$178.50
Purchase #6	$128.71	11.645%	$143.6983	$143.70	$143.70	$143.70
Purchase #7	$132.89	7.361%	$142.672	$142.67	$142.65	$142.70
7 purchase totals =	$954.56		$1,063.8861	$1,063.89	$1,063.85	$1,064.00