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 $60.73   8.716%   $66.0232   $66.02   $66.00   $66.00  
  Purchase #2 $31.81   12.688%   $35.8461   $35.85   $35.85   $35.80  
  Purchase #3 $44.26   8.165%   $47.8738   $47.87   $47.85   $47.90  
  Purchase #4 $122.81   10.368%   $135.5429   $135.54   $135.55   $135.50  
  Purchase #5 $56.26   9.667%   $61.6987   $61.70   $61.70   $61.70  
  Purchase #6 $247.59   3.273%   $255.6936   $255.69   $255.70   $255.70  
  Purchase #7 $148.30   10.307%   $163.5853   $163.59   $163.60   $163.60  
  7 purchase totals = $711.76       $766.2636   $766.26   $766.25   $766.20