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	$54.40	3.618%	$56.3682	$56.37	$56.35	$56.40
Purchase #2	$144.25	6.398%	$153.4791	$153.48	$153.50	$153.50
Purchase #3	$89.42	11.576%	$99.7713	$99.77	$99.75	$99.80
Purchase #4	$126.92	13.132%	$143.5871	$143.59	$143.60	$143.60
Purchase #5	$53.63	4.308%	$55.9404	$55.94	$55.95	$55.90
Purchase #6	$68.45	5.105%	$71.9444	$71.94	$71.95	$71.90
Purchase #7	$62.42	7.259%	$66.9511	$66.95	$66.95	$67.00
7 purchase totals =	$599.49		$648.0416	$648.04	$648.05	$648.10