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 $248.46   5.276%   $261.5687   $261.57   $261.55   $261.60  
  Purchase #2 $25.62   6.857%   $27.3768   $27.38   $27.40   $27.40  
  Purchase #3 $60.34   8.628%   $65.5461   $65.55   $65.55   $65.50  
  Purchase #4 $134.53   9.604%   $147.4503   $147.45   $147.45   $147.50  
  Purchase #5 $68.79   12.392%   $77.3145   $77.31   $77.30   $77.30  
  Purchase #6 $235.55   9.505%   $257.939   $257.94   $257.95   $257.90  
  Purchase #7 $14.30   8.569%   $15.5254   $15.53   $15.55   $15.50  
  7 purchase totals = $787.59       $852.7208   $852.73   $852.75   $852.70