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	$28.27	11.758%	$31.594	$31.59	$31.60	$31.60
Purchase #2	$249.36	12.477%	$280.4726	$280.47	$280.45	$280.50
Purchase #3	$55.64	8.277%	$60.2453	$60.25	$60.25	$60.20
Purchase #4	$51.69	4.256%	$53.8899	$53.89	$53.90	$53.90
Purchase #5	$79.88	8.440%	$86.6219	$86.62	$86.60	$86.60
Purchase #6	$132.41	8.483%	$143.6423	$143.64	$143.65	$143.60
Purchase #7	$100.88	8.476%	$109.4306	$109.43	$109.45	$109.40
7 purchase totals =	$698.13		$765.8966	$765.89	$765.90	$765.80