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	$150.63	3.573%	$156.012	$156.01	$156.00	$156.00
Purchase #2	$11.98	12.618%	$13.4916	$13.49	$13.50	$13.50
Purchase #3	$80.44	11.189%	$89.4404	$89.44	$89.45	$89.40
Purchase #4	$37.54	7.180%	$40.2354	$40.24	$40.25	$40.20
Purchase #5	$136.47	13.275%	$154.5864	$154.59	$154.60	$154.60
Purchase #6	$112.30	6.301%	$119.376	$119.38	$119.40	$119.40
Purchase #7	$246.95	13.745%	$280.8933	$280.89	$280.90	$280.90
7 purchase totals =	$776.31		$854.0351	$854.04	$854.10	$854.00