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 $91.95   4.593%   $96.1733   $96.17   $96.15   $96.20  
  Purchase #2 $248.66   10.746%   $275.381   $275.38   $275.40   $275.40  
  Purchase #3 $232.63   12.517%   $261.7483   $261.75   $261.75   $261.70  
  Purchase #4 $167.53   12.627%   $188.684   $188.68   $188.70   $188.70  
  Purchase #5 $178.81   11.176%   $198.7938   $198.79   $198.80   $198.80  
  Purchase #6 $37.49   4.556%   $39.198   $39.20   $39.20   $39.20  
  Purchase #7 $8.73   6.732%   $9.3177   $9.32   $9.30   $9.30  
  7 purchase totals = $965.80       $1,069.2961   $1,069.29   $1,069.30   $1,069.30