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 $114.66   3.423%   $118.5848   $118.58   $118.60   $118.60  
  Purchase #2 $97.55   8.366%   $105.711   $105.71   $105.70   $105.70  
  Purchase #3 $230.72   3.844%   $239.5889   $239.59   $239.60   $239.60  
  Purchase #4 $149.34   6.363%   $158.8425   $158.84   $158.85   $158.80  
  Purchase #5 $90.32   3.187%   $93.1985   $93.20   $93.20   $93.20  
  Purchase #6 $149.81   5.316%   $157.7739   $157.77   $157.75   $157.80  
  Purchase #7 $75.71   5.526%   $79.8937   $79.89   $79.90   $79.90  
  7 purchase totals = $908.11       $953.5933   $953.58   $953.60   $953.60