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	$226.61	11.159%	$251.8974	$251.90	$251.90	$251.90
Purchase #2	$180.42	3.560%	$186.843	$186.84	$186.85	$186.80
Purchase #3	$101.83	6.406%	$108.3532	$108.35	$108.35	$108.40
Purchase #4	$126.64	12.124%	$141.9938	$141.99	$142.00	$142.00
Purchase #5	$37.50	5.147%	$39.4301	$39.43	$39.45	$39.40
Purchase #6	$131.67	8.527%	$142.8975	$142.90	$142.90	$142.90
Purchase #7	$112.96	12.776%	$127.3918	$127.39	$127.40	$127.40
7 purchase totals =	$917.63		$998.8068	$998.80	$998.85	$998.80