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 $61.42   11.810%   $68.6737   $68.67   $68.65   $68.70  
  Purchase #2 $10.63   6.816%   $11.3545   $11.35   $11.35   $11.40  
  Purchase #3 $126.50   3.786%   $131.2893   $131.29   $131.30   $131.30  
  Purchase #4 $24.88   4.650%   $26.0369   $26.04   $26.05   $26.00  
  Purchase #5 $242.51   6.863%   $259.1535   $259.15   $259.15   $259.20  
  Purchase #6 $229.36   7.766%   $247.1721   $247.17   $247.15   $247.20  
  Purchase #7 $197.77   7.604%   $212.8084   $212.81   $212.80   $212.80  
  7 purchase totals = $893.07       $956.4884   $956.48   $956.45   $956.60