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	$246.90	10.782%	$273.5208	$273.52	$273.50	$273.50
Purchase #2	$75.79	3.663%	$78.5662	$78.57	$78.55	$78.60
Purchase #3	$164.59	6.691%	$175.6027	$175.60	$175.60	$175.60
Purchase #4	$198.76	4.606%	$207.9149	$207.91	$207.90	$207.90
Purchase #5	$126.71	12.117%	$142.0635	$142.06	$142.05	$142.10
Purchase #6	$240.45	8.699%	$261.3667	$261.37	$261.35	$261.40
Purchase #7	$186.63	7.238%	$200.1383	$200.14	$200.15	$200.10
7 purchase totals =	$1,239.83		$1,339.1731	$1,339.17	$1,339.10	$1,339.20