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	$69.66	7.356%	$74.7842	$74.78	$74.80	$74.80
Purchase #2	$63.82	3.758%	$66.2184	$66.22	$66.20	$66.20
Purchase #3	$37.33	12.617%	$42.0399	$42.04	$42.05	$42.00
Purchase #4	$75.57	13.174%	$85.5256	$85.53	$85.55	$85.50
Purchase #5	$72.25	13.535%	$82.029	$82.03	$82.05	$82.00
Purchase #6	$137.85	4.677%	$144.2972	$144.30	$144.30	$144.30
Purchase #7	$100.96	13.108%	$114.1938	$114.19	$114.20	$114.20
7 purchase totals =	$557.44		$609.0881	$609.09	$609.15	$609.00