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 $42.46   13.431%   $48.1628   $48.16   $48.15   $48.20  
  Purchase #2 $124.98   12.680%   $140.8275   $140.83   $140.85   $140.80  
  Purchase #3 $73.85   9.721%   $81.029   $81.03   $81.05   $81.00  
  Purchase #4 $233.31   10.287%   $257.3106   $257.31   $257.30   $257.30  
  Purchase #5 $201.71   13.283%   $228.5031   $228.50   $228.50   $228.50  
  Purchase #6 $246.37   13.859%   $280.5144   $280.51   $280.50   $280.50  
  Purchase #7 $60.63   10.307%   $66.8791   $66.88   $66.90   $66.90  
  7 purchase totals = $983.31       $1,103.2265   $1,103.22   $1,103.25   $1,103.20