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	$242.93	11.829%	$271.6662	$271.67	$271.65	$271.70
Purchase #2	$239.56	4.191%	$249.6	$249.60	$249.60	$249.60
Purchase #3	$72.50	7.638%	$78.0376	$78.04	$78.05	$78.00
Purchase #4	$123.38	10.651%	$136.5212	$136.52	$136.50	$136.50
Purchase #5	$128.26	7.285%	$137.6037	$137.60	$137.60	$137.60
Purchase #6	$244.82	9.174%	$267.2798	$267.28	$267.30	$267.30
Purchase #7	$128.71	10.242%	$141.8925	$141.89	$141.90	$141.90
7 purchase totals =	$1,180.16		$1,282.6010	$1,282.60	$1,282.60	$1,282.60