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 $57.88   3.276%   $59.7761   $59.78   $59.80   $59.80  
  Purchase #2 $240.99   10.679%   $266.7253   $266.73   $266.75   $266.70  
  Purchase #3 $112.77   4.799%   $118.1818   $118.18   $118.20   $118.20  
  Purchase #4 $12.89   5.303%   $13.5736   $13.57   $13.55   $13.60  
  Purchase #5 $88.64   13.856%   $100.922   $100.92   $100.90   $100.90  
  Purchase #6 $245.97   6.441%   $261.8129   $261.81   $261.80   $261.80  
  Purchase #7 $239.56   4.861%   $251.205   $251.21   $251.20   $251.20  
  7 purchase totals = $998.70       $1,072.1967   $1,072.20   $1,072.20   $1,072.20