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 $52.60   5.832%   $55.6676   $55.67   $55.65   $55.70  
  Purchase #2 $208.57   8.654%   $226.6196   $226.62   $226.60   $226.60  
  Purchase #3 $87.74   11.153%   $97.5256   $97.53   $97.55   $97.50  
  Purchase #4 $175.52   4.235%   $182.9533   $182.95   $182.95   $183.00  
  Purchase #5 $88.73   10.782%   $98.2969   $98.30   $98.30   $98.30  
  Purchase #6 $124.27   5.455%   $131.0489   $131.05   $131.05   $131.00  
  Purchase #7 $141.63   12.770%   $159.7162   $159.72   $159.70   $159.70  
  7 purchase totals = $879.06       $951.8281   $951.84   $951.80   $951.80