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 $68.66   6.669%   $73.2389   $73.24   $73.25   $73.20  
  Purchase #2 $196.49   10.207%   $216.5457   $216.55   $216.55   $216.50  
  Purchase #3 $108.52   5.108%   $114.0632   $114.06   $114.05   $114.10  
  Purchase #4 $187.51   5.563%   $197.9412   $197.94   $197.95   $197.90  
  Purchase #5 $17.89   9.146%   $19.5262   $19.53   $19.55   $19.50  
  Purchase #6 $56.52   4.774%   $59.2183   $59.22   $59.20   $59.20  
  Purchase #7 $133.75   5.193%   $140.6956   $140.70   $140.70   $140.70  
  7 purchase totals = $769.34       $821.2291   $821.24   $821.25   $821.10