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 $232.92   12.272%   $261.5039   $261.50   $261.50   $261.50  
  Purchase #2 $164.78   13.332%   $186.7485   $186.75   $186.75   $186.70  
  Purchase #3 $92.41   5.575%   $97.5619   $97.56   $97.55   $97.60  
  Purchase #4 $133.39   12.441%   $149.985   $149.99   $150.00   $150.00  
  Purchase #5 $193.29   4.723%   $202.4191   $202.42   $202.40   $202.40  
  Purchase #6 $124.40   11.417%   $138.6027   $138.60   $138.60   $138.60  
  Purchase #7 $63.91   3.189%   $65.9481   $65.95   $65.95   $65.90  
  7 purchase totals = $1,005.10       $1,102.7692   $1,102.77   $1,102.75   $1,102.70