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	$12.88	7.819%	$13.8871	$13.89	$13.90	$13.90
Purchase #2	$73.58	12.748%	$82.96	$82.96	$82.95	$83.00
Purchase #3	$66.57	8.225%	$72.0454	$72.05	$72.05	$72.00
Purchase #4	$42.71	7.796%	$46.0397	$46.04	$46.05	$46.00
Purchase #5	$217.65	4.710%	$227.9013	$227.90	$227.90	$227.90
Purchase #6	$107.59	6.289%	$114.3563	$114.36	$114.35	$114.40
Purchase #7	$95.84	8.602%	$104.0842	$104.08	$104.10	$104.10
7 purchase totals =	$616.82		$661.2740	$661.28	$661.30	$661.30