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	$215.29	11.456%	$239.9536	$239.95	$239.95	$240.00
Purchase #2	$159.53	5.428%	$168.1893	$168.19	$168.20	$168.20
Purchase #3	$236.52	11.133%	$262.8518	$262.85	$262.85	$262.90
Purchase #4	$22.47	10.727%	$24.8804	$24.88	$24.90	$24.90
Purchase #5	$137.51	11.205%	$152.918	$152.92	$152.90	$152.90
Purchase #6	$217.72	7.449%	$233.938	$233.94	$233.95	$233.90
Purchase #7	$140.43	10.801%	$155.5978	$155.60	$155.60	$155.60
7 purchase totals =	$1,129.47		$1,238.3289	$1,238.33	$1,238.35	$1,238.40