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 $82.51   13.771%   $93.8725   $93.87   $93.85   $93.90  
  Purchase #2 $83.99   13.490%   $95.3203   $95.32   $95.30   $95.30  
  Purchase #3 $117.34   4.386%   $122.4865   $122.49   $122.50   $122.50  
  Purchase #4 $35.36   9.224%   $38.6216   $38.62   $38.60   $38.60  
  Purchase #5 $139.54   13.500%   $158.3779   $158.38   $158.40   $158.40  
  Purchase #6 $179.25   8.538%   $194.5544   $194.55   $194.55   $194.60  
  Purchase #7 $48.78   13.383%   $55.3082   $55.31   $55.30   $55.30  
  7 purchase totals = $686.77       $758.5414   $758.54   $758.50   $758.60