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	$139.50	12.159%	$156.4618	$156.46	$156.45	$156.50
Purchase #2	$43.86	10.447%	$48.4421	$48.44	$48.45	$48.40
Purchase #3	$30.83	7.303%	$33.0815	$33.08	$33.10	$33.10
Purchase #4	$86.55	3.520%	$89.5966	$89.60	$89.60	$89.60
Purchase #5	$153.69	12.314%	$172.6154	$172.62	$172.60	$172.60
Purchase #6	$89.96	10.520%	$99.4238	$99.42	$99.40	$99.40
Purchase #7	$131.81	9.832%	$144.7696	$144.77	$144.75	$144.80
7 purchase totals =	$676.20		$744.3908	$744.39	$744.35	$744.40