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 $232.89   12.443%   $261.8685   $261.87   $261.85   $261.90  
  Purchase #2 $191.59   6.666%   $204.3614   $204.36   $204.35   $204.40  
  Purchase #3 $17.89   7.257%   $19.1883   $19.19   $19.20   $19.20  
  Purchase #4 $61.25   9.393%   $67.0032   $67.00   $67.00   $67.00  
  Purchase #5 $52.41   6.795%   $55.9713   $55.97   $55.95   $56.00  
  Purchase #6 $182.84   12.299%   $205.3275   $205.33   $205.35   $205.30  
  Purchase #7 $144.72   3.141%   $149.2657   $149.27   $149.25   $149.30  
  7 purchase totals = $883.59       $962.9859   $962.99   $962.95   $963.10