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 $109.93   11.871%   $122.9798   $122.98   $123.00   $123.00  
  Purchase #2 $142.39   11.872%   $159.2945   $159.29   $159.30   $159.30  
  Purchase #3 $57.63   12.873%   $65.0487   $65.05   $65.05   $65.00  
  Purchase #4 $144.44   7.511%   $155.2889   $155.29   $155.30   $155.30  
  Purchase #5 $53.97   10.211%   $59.4809   $59.48   $59.50   $59.50  
  Purchase #6 $56.76   6.421%   $60.4046   $60.40   $60.40   $60.40  
  Purchase #7 $246.66   5.823%   $261.023   $261.02   $261.00   $261.00  
  7 purchase totals = $811.78       $883.5204   $883.51   $883.55   $883.50