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 $235.64   13.822%   $268.2102   $268.21   $268.20   $268.20  
  Purchase #2 $31.90   4.324%   $33.2794   $33.28   $33.30   $33.30  
  Purchase #3 $122.89   12.744%   $138.5511   $138.55   $138.55   $138.60  
  Purchase #4 $84.79   10.708%   $93.8693   $93.87   $93.85   $93.90  
  Purchase #5 $64.76   4.174%   $67.4631   $67.46   $67.45   $67.50  
  Purchase #6 $210.97   11.256%   $234.7168   $234.72   $234.70   $234.70  
  Purchase #7 $144.40   9.678%   $158.375   $158.38   $158.40   $158.40  
  7 purchase totals = $895.35       $994.4649   $994.47   $994.45   $994.60