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	$224.52	13.606%	$255.0682	$255.07	$255.05	$255.10
Purchase #2	$224.48	6.223%	$238.4494	$238.45	$238.45	$238.40
Purchase #3	$87.45	7.574%	$94.0735	$94.07	$94.05	$94.10
Purchase #4	$42.82	11.823%	$47.8826	$47.88	$47.90	$47.90
Purchase #5	$172.74	5.868%	$182.8764	$182.88	$182.90	$182.90
Purchase #6	$7.39	3.855%	$7.6749	$7.67	$7.65	$7.70
Purchase #7	$23.31	8.304%	$25.2457	$25.25	$25.25	$25.20
7 purchase totals =	$782.71		$851.2707	$851.27	$851.25	$851.30