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 $63.28   4.709%   $66.2599   $66.26   $66.25   $66.30  
  Purchase #2 $78.36   5.782%   $82.8908   $82.89   $82.90   $82.90  
  Purchase #3 $31.26   8.653%   $33.9649   $33.96   $33.95   $34.00  
  Purchase #4 $58.46   13.648%   $66.4386   $66.44   $66.45   $66.40  
  Purchase #5 $129.75   5.364%   $136.7098   $136.71   $136.70   $136.70  
  Purchase #6 $204.83   5.648%   $216.3988   $216.40   $216.40   $216.40  
  Purchase #7 $110.72   5.821%   $117.165   $117.17   $117.15   $117.20  
  7 purchase totals = $676.66       $719.8278   $719.83   $719.80   $719.90