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	$119.72	9.661%	$131.2861	$131.29	$131.30	$131.30
Purchase #2	$143.47	8.853%	$156.1714	$156.17	$156.15	$156.20
Purchase #3	$246.92	13.488%	$280.2246	$280.22	$280.20	$280.20
Purchase #4	$38.59	12.606%	$43.4547	$43.45	$43.45	$43.50
Purchase #5	$42.36	10.481%	$46.7998	$46.80	$46.80	$46.80
Purchase #6	$43.99	6.215%	$46.724	$46.72	$46.70	$46.70
Purchase #7	$200.61	3.468%	$207.5672	$207.57	$207.55	$207.60
7 purchase totals =	$835.66		$912.2278	$912.22	$912.15	$912.30