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 $71.99   6.558%   $76.7111   $76.71   $76.70   $76.70  
  Purchase #2 $179.87   13.379%   $203.9348   $203.93   $203.95   $203.90  
  Purchase #3 $48.89   8.262%   $52.9293   $52.93   $52.95   $52.90  
  Purchase #4 $110.81   7.449%   $119.0642   $119.06   $119.05   $119.10  
  Purchase #5 $97.36   8.718%   $105.8478   $105.85   $105.85   $105.80  
  Purchase #6 $65.55   8.854%   $71.3538   $71.35   $71.35   $71.40  
  Purchase #7 $91.72   12.114%   $102.831   $102.83   $102.85   $102.80  
  7 purchase totals = $666.19       $732.6720   $732.66   $732.70   $732.60