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	$51.85	7.113%	$55.5381	$55.54	$55.55	$55.50
Purchase #2	$207.65	12.734%	$234.0922	$234.09	$234.10	$234.10
Purchase #3	$78.89	12.289%	$88.5848	$88.58	$88.60	$88.60
Purchase #4	$174.78	11.228%	$194.4043	$194.40	$194.40	$194.40
Purchase #5	$216.47	10.154%	$238.4504	$238.45	$238.45	$238.50
Purchase #6	$46.85	11.292%	$52.1403	$52.14	$52.15	$52.10
Purchase #7	$114.72	11.119%	$127.4757	$127.48	$127.50	$127.50
7 purchase totals =	$891.21		$990.6858	$990.68	$990.75	$990.70