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 $60.92   8.861%   $66.3181   $66.32   $66.30   $66.30  
  Purchase #2 $166.99   11.536%   $186.254   $186.25   $186.25   $186.30  
  Purchase #3 $177.57   4.588%   $185.7169   $185.72   $185.70   $185.70  
  Purchase #4 $228.36   11.634%   $254.9274   $254.93   $254.95   $254.90  
  Purchase #5 $41.71   7.480%   $44.8299   $44.83   $44.85   $44.80  
  Purchase #6 $93.62   9.257%   $102.2864   $102.29   $102.30   $102.30  
  Purchase #7 $112.85   5.762%   $119.3524   $119.35   $119.35   $119.40  
  7 purchase totals = $882.02       $959.6851   $959.69   $959.70   $959.70