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	$241.53	12.856%	$272.5811	$272.58	$272.60	$272.60
Purchase #2	$203.83	13.617%	$231.5855	$231.59	$231.60	$231.60
Purchase #3	$166.32	11.541%	$185.515	$185.52	$185.50	$185.50
Purchase #4	$37.92	6.378%	$40.3385	$40.34	$40.35	$40.30
Purchase #5	$205.28	6.638%	$218.9065	$218.91	$218.90	$218.90
Purchase #6	$47.59	8.201%	$51.4929	$51.49	$51.50	$51.50
Purchase #7	$195.72	6.328%	$208.1052	$208.11	$208.10	$208.10
7 purchase totals =	$1,098.19		$1,208.5247	$1,208.54	$1,208.55	$1,208.50