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	$126.59	13.294%	$143.4189	$143.42	$143.40	$143.40
Purchase #2	$38.83	12.159%	$43.5513	$43.55	$43.55	$43.60
Purchase #3	$238.92	4.266%	$249.1123	$249.11	$249.10	$249.10
Purchase #4	$6.95	10.621%	$7.6882	$7.69	$7.70	$7.70
Purchase #5	$246.57	13.837%	$280.6879	$280.69	$280.70	$280.70
Purchase #6	$119.72	6.665%	$127.6993	$127.70	$127.70	$127.70
Purchase #7	$39.47	9.759%	$43.3219	$43.32	$43.30	$43.30
7 purchase totals =	$817.05		$895.4798	$895.48	$895.45	$895.50