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	$208.36	6.770%	$222.466	$222.47	$222.45	$222.50
Purchase #2	$41.90	11.226%	$46.6037	$46.60	$46.60	$46.60
Purchase #3	$247.29	10.670%	$273.6758	$273.68	$273.70	$273.70
Purchase #4	$221.81	11.168%	$246.5817	$246.58	$246.60	$246.60
Purchase #5	$164.90	8.494%	$178.9066	$178.91	$178.90	$178.90
Purchase #6	$150.71	11.372%	$167.8487	$167.85	$167.85	$167.80
Purchase #7	$155.49	11.836%	$173.8938	$173.89	$173.90	$173.90
7 purchase totals =	$1,190.46		$1,309.9763	$1,309.98	$1,310.00	$1,310.00