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	$242.61	5.341%	$255.5678	$255.57	$255.55	$255.60
Purchase #2	$243.96	8.742%	$265.287	$265.29	$265.30	$265.30
Purchase #3	$34.71	7.613%	$37.3525	$37.35	$37.35	$37.40
Purchase #4	$126.49	10.796%	$140.1459	$140.15	$140.15	$140.10
Purchase #5	$76.37	12.393%	$85.8345	$85.83	$85.85	$85.80
Purchase #6	$137.85	12.337%	$154.8566	$154.86	$154.85	$154.90
Purchase #7	$128.96	4.481%	$134.7387	$134.74	$134.75	$134.70
7 purchase totals =	$990.95		$1,073.7830	$1,073.79	$1,073.80	$1,073.80