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	$37.84	6.206%	$40.1884	$40.19	$40.20	$40.20
Purchase #2	$118.51	6.593%	$126.3234	$126.32	$126.30	$126.30
Purchase #3	$237.43	8.150%	$256.7805	$256.78	$256.80	$256.80
Purchase #4	$127.84	12.503%	$143.8238	$143.82	$143.80	$143.80
Purchase #5	$171.57	9.429%	$187.7473	$187.75	$187.75	$187.70
Purchase #6	$126.61	11.734%	$141.4664	$141.47	$141.45	$141.50
Purchase #7	$235.60	6.458%	$250.815	$250.82	$250.80	$250.80
7 purchase totals =	$1,055.40		$1,147.1448	$1,147.15	$1,147.10	$1,147.10