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	$248.60	12.788%	$280.391	$280.39	$280.40	$280.40
Purchase #2	$204.49	4.294%	$213.2708	$213.27	$213.25	$213.30
Purchase #3	$115.78	6.717%	$123.5569	$123.56	$123.55	$123.60
Purchase #4	$228.43	7.788%	$246.2201	$246.22	$246.20	$246.20
Purchase #5	$199.71	10.191%	$220.0624	$220.06	$220.05	$220.10
Purchase #6	$28.95	12.291%	$32.5082	$32.51	$32.50	$32.50
Purchase #7	$36.87	5.365%	$38.8481	$38.85	$38.85	$38.80
7 purchase totals =	$1,062.83		$1,154.8575	$1,154.86	$1,154.80	$1,154.90