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	$245.36	11.293%	$273.0685	$273.07	$273.05	$273.10
Purchase #2	$131.81	4.255%	$137.4185	$137.42	$137.40	$137.40
Purchase #3	$80.97	7.317%	$86.8946	$86.89	$86.90	$86.90
Purchase #4	$66.29	8.847%	$72.1547	$72.15	$72.15	$72.20
Purchase #5	$144.86	13.238%	$164.0366	$164.04	$164.05	$164.00
Purchase #6	$133.67	8.378%	$144.8689	$144.87	$144.85	$144.90
Purchase #7	$13.49	7.126%	$14.4513	$14.45	$14.45	$14.50
7 purchase totals =	$816.45		$892.8931	$892.89	$892.85	$893.00