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 $34.68   7.207%   $37.1794   $37.18   $37.20   $37.20  
  Purchase #2 $244.84   6.814%   $261.5234   $261.52   $261.50   $261.50  
  Purchase #3 $167.39   12.631%   $188.533   $188.53   $188.55   $188.50  
  Purchase #4 $153.95   5.588%   $162.5527   $162.55   $162.55   $162.60  
  Purchase #5 $127.93   8.341%   $138.6006   $138.60   $138.60   $138.60  
  Purchase #6 $6.77   5.392%   $7.135   $7.14   $7.15   $7.10  
  Purchase #7 $183.87   13.317%   $208.356   $208.36   $208.35   $208.40  
  7 purchase totals = $919.43       $1,003.8801   $1,003.88   $1,003.90   $1,003.90