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	$49.83	13.354%	$56.4843	$56.48	$56.50	$56.50
Purchase #2	$105.60	3.770%	$109.5811	$109.58	$109.60	$109.60
Purchase #3	$127.88	9.535%	$140.0734	$140.07	$140.05	$140.10
Purchase #4	$158.48	8.355%	$171.721	$171.72	$171.70	$171.70
Purchase #5	$7.78	12.759%	$8.7727	$8.77	$8.75	$8.80
Purchase #6	$205.90	10.672%	$227.8736	$227.87	$227.85	$227.90
Purchase #7	$130.80	13.628%	$148.6254	$148.63	$148.65	$148.60
7 purchase totals =	$786.27		$863.1315	$863.12	$863.10	$863.20