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	$123.67	6.401%	$131.5861	$131.59	$131.60	$131.60
Purchase #2	$178.99	12.131%	$200.7033	$200.70	$200.70	$200.70
Purchase #3	$227.56	3.394%	$235.2834	$235.28	$235.30	$235.30
Purchase #4	$230.65	13.372%	$261.4925	$261.49	$261.50	$261.50
Purchase #5	$156.42	7.862%	$168.7177	$168.72	$168.70	$168.70
Purchase #6	$164.43	12.835%	$185.5346	$185.53	$185.55	$185.50
Purchase #7	$156.91	12.767%	$176.9427	$176.94	$176.95	$176.90
7 purchase totals =	$1,238.63		$1,360.2603	$1,360.25	$1,360.30	$1,360.20