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	$245.98	12.161%	$275.8936	$275.89	$275.90	$275.90
Purchase #2	$39.45	3.281%	$40.7444	$40.74	$40.75	$40.70
Purchase #3	$220.47	3.211%	$227.5493	$227.55	$227.55	$227.50
Purchase #4	$56.53	8.673%	$61.4328	$61.43	$61.45	$61.40
Purchase #5	$213.30	3.351%	$220.4477	$220.45	$220.45	$220.40
Purchase #6	$236.50	10.528%	$261.3987	$261.40	$261.40	$261.40
Purchase #7	$37.51	13.554%	$42.5941	$42.59	$42.60	$42.60
7 purchase totals =	$1,049.74		$1,130.0606	$1,130.05	$1,130.10	$1,129.90