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	$29.60	7.842%	$31.9212	$31.92	$31.90	$31.90
Purchase #2	$61.69	3.396%	$63.785	$63.79	$63.80	$63.80
Purchase #3	$166.84	12.580%	$187.8285	$187.83	$187.85	$187.80
Purchase #4	$225.67	5.639%	$238.3955	$238.40	$238.40	$238.40
Purchase #5	$84.42	9.814%	$92.705	$92.71	$92.70	$92.70
Purchase #6	$104.37	7.665%	$112.37	$112.37	$112.35	$112.40
Purchase #7	$33.63	11.406%	$37.4658	$37.47	$37.45	$37.50
7 purchase totals =	$706.22		$764.4710	$764.49	$764.45	$764.50