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	$85.78	3.292%	$88.6039	$88.60	$88.60	$88.60
Purchase #2	$216.44	9.805%	$237.6619	$237.66	$237.65	$237.70
Purchase #3	$106.53	4.606%	$111.4368	$111.44	$111.45	$111.40
Purchase #4	$100.85	13.529%	$114.494	$114.49	$114.50	$114.50
Purchase #5	$35.55	11.806%	$39.747	$39.75	$39.75	$39.70
Purchase #6	$40.37	5.509%	$42.594	$42.59	$42.60	$42.60
Purchase #7	$26.86	12.832%	$30.3067	$30.31	$30.30	$30.30
7 purchase totals =	$612.38		$664.8443	$664.84	$664.85	$664.80