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	$94.64	6.520%	$100.8105	$100.81	$100.80	$100.80
Purchase #2	$208.89	7.826%	$225.2377	$225.24	$225.25	$225.20
Purchase #3	$103.91	5.308%	$109.4255	$109.43	$109.45	$109.40
Purchase #4	$50.95	13.519%	$57.8379	$57.84	$57.85	$57.80
Purchase #5	$235.32	8.679%	$255.7434	$255.74	$255.75	$255.70
Purchase #6	$55.26	4.611%	$57.808	$57.81	$57.80	$57.80
Purchase #7	$47.26	9.724%	$51.8556	$51.86	$51.85	$51.90
7 purchase totals =	$796.23		$858.7186	$858.73	$858.75	$858.60