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	$217.58	3.612%	$225.439	$225.44	$225.45	$225.40
Purchase #2	$155.65	8.433%	$168.776	$168.78	$168.80	$168.80
Purchase #3	$141.55	11.841%	$158.3109	$158.31	$158.30	$158.30
Purchase #4	$238.82	12.112%	$267.7459	$267.75	$267.75	$267.70
Purchase #5	$20.50	13.854%	$23.3401	$23.34	$23.35	$23.30
Purchase #6	$85.65	5.268%	$90.162	$90.16	$90.15	$90.20
Purchase #7	$51.75	9.598%	$56.717	$56.72	$56.70	$56.70
7 purchase totals =	$911.50		$990.4909	$990.50	$990.50	$990.40