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	$142.55	10.486%	$157.4978	$157.50	$157.50	$157.50
Purchase #2	$31.43	10.807%	$34.8266	$34.83	$34.85	$34.80
Purchase #3	$65.76	4.188%	$68.514	$68.51	$68.50	$68.50
Purchase #4	$123.81	3.295%	$127.8895	$127.89	$127.90	$127.90
Purchase #5	$27.72	8.316%	$30.0252	$30.03	$30.05	$30.00
Purchase #6	$236.95	7.763%	$255.3444	$255.34	$255.35	$255.30
Purchase #7	$185.89	13.398%	$210.7955	$210.80	$210.80	$210.80
7 purchase totals =	$814.11		$884.8930	$884.90	$884.95	$884.80