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	$67.29	4.663%	$70.4277	$70.43	$70.45	$70.40
Purchase #2	$93.53	7.477%	$100.5232	$100.52	$100.50	$100.50
Purchase #3	$199.31	3.215%	$205.7178	$205.72	$205.70	$205.70
Purchase #4	$93.69	5.700%	$99.0303	$99.03	$99.05	$99.00
Purchase #5	$46.42	11.129%	$51.5861	$51.59	$51.60	$51.60
Purchase #6	$87.82	12.369%	$98.6825	$98.68	$98.70	$98.70
Purchase #7	$245.63	4.801%	$257.4227	$257.42	$257.40	$257.40
7 purchase totals =	$833.69		$883.3903	$883.39	$883.40	$883.30