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 $57.67   3.488%   $59.6815   $59.68   $59.70   $59.70  
  Purchase #2 $128.47   6.847%   $137.2663   $137.27   $137.25   $137.30  
  Purchase #3 $35.25   13.583%   $40.038   $40.04   $40.05   $40.00  
  Purchase #4 $206.27   9.549%   $225.9667   $225.97   $225.95   $226.00  
  Purchase #5 $113.39   10.854%   $125.6974   $125.70   $125.70   $125.70  
  Purchase #6 $104.88   4.165%   $109.2483   $109.25   $109.25   $109.20  
  Purchase #7 $50.73   12.189%   $56.9135   $56.91   $56.90   $56.90  
  7 purchase totals = $696.66       $754.8117   $754.82   $754.80   $754.80