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	$123.87	3.759%	$128.5263	$128.53	$128.55	$128.50
Purchase #2	$85.74	10.262%	$94.5386	$94.54	$94.55	$94.50
Purchase #3	$44.69	6.277%	$47.4952	$47.50	$47.50	$47.50
Purchase #4	$99.94	9.622%	$109.5562	$109.56	$109.55	$109.60
Purchase #5	$194.27	5.828%	$205.5921	$205.59	$205.60	$205.60
Purchase #6	$131.42	8.308%	$142.3384	$142.34	$142.35	$142.30
Purchase #7	$205.25	4.771%	$215.0425	$215.04	$215.05	$215.00
7 purchase totals =	$885.18		$943.0893	$943.10	$943.15	$943.00