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 $68.31   8.104%   $73.8458   $73.85   $73.85   $73.80  
  Purchase #2 $229.62   8.312%   $248.706   $248.71   $248.70   $248.70  
  Purchase #3 $190.39   7.709%   $205.0672   $205.07   $205.05   $205.10  
  Purchase #4 $104.28   8.305%   $112.9405   $112.94   $112.95   $112.90  
  Purchase #5 $21.30   12.526%   $23.968   $23.97   $23.95   $24.00  
  Purchase #6 $39.91   13.656%   $45.3601   $45.36   $45.35   $45.40  
  Purchase #7 $161.44   8.387%   $174.98   $174.98   $175.00   $175.00  
  7 purchase totals = $815.25       $884.8676   $884.88   $884.85   $884.90