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	$228.70	12.138%	$256.4596	$256.46	$256.45	$256.50
Purchase #2	$64.85	13.361%	$73.5146	$73.51	$73.50	$73.50
Purchase #3	$124.34	12.706%	$140.1386	$140.14	$140.15	$140.10
Purchase #4	$81.68	8.508%	$88.6293	$88.63	$88.65	$88.60
Purchase #5	$239.86	6.672%	$255.8635	$255.86	$255.85	$255.90
Purchase #6	$245.64	4.611%	$256.9665	$256.97	$256.95	$257.00
Purchase #7	$99.59	3.336%	$102.9123	$102.91	$102.90	$102.90
7 purchase totals =	$1,084.66		$1,174.4844	$1,174.48	$1,174.45	$1,174.50