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 $247.54   5.726%   $261.7141   $261.71   $261.70   $261.70  
  Purchase #2 $120.40   10.859%   $133.4742   $133.47   $133.45   $133.50  
  Purchase #3 $238.55   10.495%   $263.5858   $263.59   $263.60   $263.60  
  Purchase #4 $79.96   8.183%   $86.5031   $86.50   $86.50   $86.50  
  Purchase #5 $53.49   9.595%   $58.6224   $58.62   $58.60   $58.60  
  Purchase #6 $144.49   8.303%   $156.487   $156.49   $156.50   $156.50  
  Purchase #7 $66.90   12.857%   $75.5013   $75.50   $75.50   $75.50  
  7 purchase totals = $951.33       $1,035.8879   $1,035.88   $1,035.85   $1,035.90