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 $142.42   10.733%   $157.7059   $157.71   $157.70   $157.70  
  Purchase #2 $60.60   12.619%   $68.2471   $68.25   $68.25   $68.20  
  Purchase #3 $142.57   12.378%   $160.2173   $160.22   $160.20   $160.20  
  Purchase #4 $61.29   6.587%   $65.3272   $65.33   $65.35   $65.30  
  Purchase #5 $56.69   10.425%   $62.5999   $62.60   $62.60   $62.60  
  Purchase #6 $196.53   10.630%   $217.4211   $217.42   $217.40   $217.40  
  Purchase #7 $56.81   10.653%   $62.862   $62.86   $62.85   $62.90  
  7 purchase totals = $716.91       $794.3805   $794.39   $794.35   $794.30