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	$61.87	11.108%	$68.7425	$68.74	$68.75	$68.70
Purchase #2	$76.89	8.754%	$83.621	$83.62	$83.60	$83.60
Purchase #3	$246.54	13.814%	$280.597	$280.60	$280.60	$280.60
Purchase #4	$51.39	11.826%	$57.4674	$57.47	$57.45	$57.50
Purchase #5	$246.33	9.525%	$269.7929	$269.79	$269.80	$269.80
Purchase #6	$49.29	7.243%	$52.8601	$52.86	$52.85	$52.90
Purchase #7	$83.69	6.155%	$88.8411	$88.84	$88.85	$88.80
7 purchase totals =	$816.00		$901.9220	$901.92	$901.90	$901.90