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	$38.93	11.687%	$43.4797	$43.48	$43.50	$43.50
Purchase #2	$145.81	4.854%	$152.8876	$152.89	$152.90	$152.90
Purchase #3	$250.64	12.270%	$281.3935	$281.39	$281.40	$281.40
Purchase #4	$127.82	9.509%	$139.9744	$139.97	$139.95	$140.00
Purchase #5	$236.26	8.130%	$255.4679	$255.47	$255.45	$255.50
Purchase #6	$190.85	4.721%	$199.86	$199.86	$199.85	$199.90
Purchase #7	$231.51	12.632%	$260.7543	$260.75	$260.75	$260.80
7 purchase totals =	$1,221.82		$1,333.8174	$1,333.81	$1,333.80	$1,334.00