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	$131.80	6.390%	$140.222	$140.22	$140.20	$140.20
Purchase #2	$227.90	13.380%	$258.393	$258.39	$258.40	$258.40
Purchase #3	$72.38	13.424%	$82.0963	$82.10	$82.10	$82.10
Purchase #4	$10.30	5.448%	$10.8611	$10.86	$10.85	$10.90
Purchase #5	$83.32	10.187%	$91.8078	$91.81	$91.80	$91.80
Purchase #6	$163.46	8.683%	$177.6532	$177.65	$177.65	$177.70
Purchase #7	$173.26	13.622%	$196.8615	$196.86	$196.85	$196.90
7 purchase totals =	$862.42		$957.8949	$957.89	$957.85	$958.00