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	$241.33	12.534%	$271.5783	$271.58	$271.60	$271.60
Purchase #2	$79.85	12.509%	$89.8384	$89.84	$89.85	$89.80
Purchase #3	$112.55	6.147%	$119.4684	$119.47	$119.45	$119.50
Purchase #4	$12.28	10.842%	$13.6114	$13.61	$13.60	$13.60
Purchase #5	$155.72	10.500%	$172.0706	$172.07	$172.05	$172.10
Purchase #6	$135.40	10.472%	$149.5791	$149.58	$149.60	$149.60
Purchase #7	$169.67	7.620%	$182.5989	$182.60	$182.60	$182.60
7 purchase totals =	$906.80		$998.7451	$998.75	$998.75	$998.80