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 $24.46   11.733%   $27.3299   $27.33   $27.35   $27.30  
  Purchase #2 $182.78   4.730%   $191.4255   $191.43   $191.45   $191.40  
  Purchase #3 $27.70   11.525%   $30.8924   $30.89   $30.90   $30.90  
  Purchase #4 $236.66   8.708%   $257.2684   $257.27   $257.25   $257.30  
  Purchase #5 $77.55   6.797%   $82.8211   $82.82   $82.80   $82.80  
  Purchase #6 $187.47   5.560%   $197.8933   $197.89   $197.90   $197.90  
  Purchase #7 $89.54   4.388%   $93.469   $93.47   $93.45   $93.50  
  7 purchase totals = $826.16       $881.0996   $881.10   $881.10   $881.10