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 $24.87   4.571%   $26.0068   $26.01   $26.00   $26.00  
  Purchase #2 $85.58   9.202%   $93.4551   $93.46   $93.45   $93.50  
  Purchase #3 $240.54   11.262%   $267.6296   $267.63   $267.65   $267.60  
  Purchase #4 $13.49   7.767%   $14.5378   $14.54   $14.55   $14.50  
  Purchase #5 $65.48   5.227%   $68.9026   $68.90   $68.90   $68.90  
  Purchase #6 $94.55   6.829%   $101.0068   $101.01   $101.00   $101.00  
  Purchase #7 $238.73   12.211%   $267.8813   $267.88   $267.90   $267.90  
  7 purchase totals = $763.24       $839.4200   $839.43   $839.45   $839.40