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	$52.95	12.620%	$59.6323	$59.63	$59.65	$59.60
Purchase #2	$171.40	4.837%	$179.6906	$179.69	$179.70	$179.70
Purchase #3	$82.79	9.732%	$90.8471	$90.85	$90.85	$90.80
Purchase #4	$81.50	3.455%	$84.3158	$84.32	$84.30	$84.30
Purchase #5	$249.31	9.508%	$273.0144	$273.01	$273.00	$273.00
Purchase #6	$18.49	13.495%	$20.9852	$20.99	$21.00	$21.00
Purchase #7	$43.71	9.300%	$47.775	$47.78	$47.80	$47.80
7 purchase totals =	$700.15		$756.2604	$756.27	$756.30	$756.20