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 $119.51   5.642%   $126.2528   $126.25   $126.25   $126.30  
  Purchase #2 $123.85   13.341%   $140.3728   $140.37   $140.35   $140.40  
  Purchase #3 $14.44   8.802%   $15.711   $15.71   $15.70   $15.70  
  Purchase #4 $26.44   3.853%   $27.4587   $27.46   $27.45   $27.50  
  Purchase #5 $138.31   5.456%   $145.8562   $145.86   $145.85   $145.90  
  Purchase #6 $180.59   13.455%   $204.8884   $204.89   $204.90   $204.90  
  Purchase #7 $73.41   11.636%   $81.952   $81.95   $81.95   $82.00  
  7 purchase totals = $676.55       $742.4919   $742.49   $742.45   $742.70