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	$42.49	12.520%	$47.8097	$47.81	$47.80	$47.80
Purchase #2	$49.89	11.807%	$55.7805	$55.78	$55.80	$55.80
Purchase #3	$127.76	12.720%	$144.0111	$144.01	$144.00	$144.00
Purchase #4	$99.38	13.225%	$112.523	$112.52	$112.50	$112.50
Purchase #5	$114.44	8.112%	$123.7234	$123.72	$123.70	$123.70
Purchase #6	$14.71	8.272%	$15.9268	$15.93	$15.95	$15.90
Purchase #7	$130.31	9.431%	$142.5995	$142.60	$142.60	$142.60
7 purchase totals =	$578.98		$642.3740	$642.37	$642.35	$642.30