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	$118.35	13.579%	$134.4207	$134.42	$134.40	$134.40
Purchase #2	$80.86	11.319%	$90.0125	$90.01	$90.00	$90.00
Purchase #3	$192.45	9.351%	$210.446	$210.45	$210.45	$210.40
Purchase #4	$237.55	9.276%	$259.5851	$259.59	$259.60	$259.60
Purchase #5	$192.94	10.326%	$212.863	$212.86	$212.85	$212.90
Purchase #6	$154.69	13.110%	$174.9699	$174.97	$174.95	$175.00
Purchase #7	$137.79	13.644%	$156.5901	$156.59	$156.60	$156.60
7 purchase totals =	$1,114.63		$1,238.8873	$1,238.89	$1,238.85	$1,238.90