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	$228.55	11.847%	$255.6263	$255.63	$255.65	$255.60
Purchase #2	$221.46	9.499%	$242.4965	$242.50	$242.50	$242.50
Purchase #3	$75.31	4.569%	$78.7509	$78.75	$78.75	$78.80
Purchase #4	$43.83	9.288%	$47.9009	$47.90	$47.90	$47.90
Purchase #5	$168.89	5.758%	$178.6147	$178.61	$178.60	$178.60
Purchase #6	$88.94	13.154%	$100.6392	$100.64	$100.65	$100.60
Purchase #7	$63.73	12.234%	$71.5267	$71.53	$71.55	$71.50
7 purchase totals =	$890.71		$975.5552	$975.56	$975.60	$975.50