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	$105.30	6.664%	$112.3172	$112.32	$112.30	$112.30
Purchase #2	$164.47	11.308%	$183.0683	$183.07	$183.05	$183.10
Purchase #3	$40.99	13.574%	$46.554	$46.55	$46.55	$46.60
Purchase #4	$97.82	11.713%	$109.2777	$109.28	$109.30	$109.30
Purchase #5	$145.65	8.385%	$157.8628	$157.86	$157.85	$157.90
Purchase #6	$225.45	5.608%	$238.0932	$238.09	$238.10	$238.10
Purchase #7	$104.33	5.156%	$109.7093	$109.71	$109.70	$109.70
7 purchase totals =	$884.01		$956.8825	$956.88	$956.85	$957.00