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 $83.55   5.848%   $88.436   $88.44   $88.45   $88.40  
  Purchase #2 $227.70   12.324%   $255.7617   $255.76   $255.75   $255.80  
  Purchase #3 $93.87   10.692%   $103.9066   $103.91   $103.90   $103.90  
  Purchase #4 $52.27   6.288%   $55.5567   $55.56   $55.55   $55.60  
  Purchase #5 $57.61   5.489%   $60.7722   $60.77   $60.75   $60.80  
  Purchase #6 $217.94   5.823%   $230.6306   $230.63   $230.65   $230.60  
  Purchase #7 $150.63   8.839%   $163.9442   $163.94   $163.95   $163.90  
  7 purchase totals = $883.57       $959.0080   $959.01   $959.00   $959.00