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	$75.78	3.551%	$78.4709	$78.47	$78.45	$78.50
Purchase #2	$134.84	10.295%	$148.7218	$148.72	$148.70	$148.70
Purchase #3	$239.43	8.115%	$258.8597	$258.86	$258.85	$258.90
Purchase #4	$189.90	12.117%	$212.9102	$212.91	$212.90	$212.90
Purchase #5	$159.67	5.564%	$168.554	$168.55	$168.55	$168.60
Purchase #6	$39.57	4.313%	$41.2767	$41.28	$41.30	$41.30
Purchase #7	$21.26	6.267%	$22.5924	$22.59	$22.60	$22.60
7 purchase totals =	$860.45		$931.3857	$931.38	$931.35	$931.50