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 $73.94   12.182%   $82.9474   $82.95   $82.95   $82.90  
  Purchase #2 $134.52   3.578%   $139.3331   $139.33   $139.35   $139.30  
  Purchase #3 $157.89   4.270%   $164.6319   $164.63   $164.65   $164.60  
  Purchase #4 $95.70   10.616%   $105.8595   $105.86   $105.85   $105.90  
  Purchase #5 $60.91   13.728%   $69.2717   $69.27   $69.25   $69.30  
  Purchase #6 $208.26   12.801%   $234.9194   $234.92   $234.90   $234.90  
  Purchase #7 $63.81   7.728%   $68.7412   $68.74   $68.75   $68.70  
  7 purchase totals = $795.03       $865.7042   $865.70   $865.70   $865.60