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	$229.76	11.385%	$255.9182	$255.92	$255.90	$255.90
Purchase #2	$226.47	12.536%	$254.8603	$254.86	$254.85	$254.90
Purchase #3	$46.86	9.598%	$51.3576	$51.36	$51.35	$51.40
Purchase #4	$46.74	8.816%	$50.8606	$50.86	$50.85	$50.90
Purchase #5	$42.78	11.858%	$47.8529	$47.85	$47.85	$47.90
Purchase #6	$215.57	12.428%	$242.361	$242.36	$242.35	$242.40
Purchase #7	$58.88	13.457%	$66.8035	$66.80	$66.80	$66.80
7 purchase totals =	$867.06		$970.0141	$970.01	$969.95	$970.20