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	$70.43	5.793%	$74.51	$74.51	$74.50	$74.50
Purchase #2	$164.71	13.450%	$186.8635	$186.86	$186.85	$186.90
Purchase #3	$39.48	8.421%	$42.8046	$42.80	$42.80	$42.80
Purchase #4	$144.83	6.209%	$153.8225	$153.82	$153.80	$153.80
Purchase #5	$29.89	5.105%	$31.4159	$31.42	$31.40	$31.40
Purchase #6	$244.79	8.756%	$266.2238	$266.22	$266.20	$266.20
Purchase #7	$95.54	5.436%	$100.7336	$100.73	$100.75	$100.70
7 purchase totals =	$789.67		$856.3739	$856.36	$856.30	$856.30