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 $90.67   5.312%   $95.4864   $95.49   $95.50   $95.50  
  Purchase #2 $233.81   9.551%   $256.1412   $256.14   $256.15   $256.10  
  Purchase #3 $33.43   13.823%   $38.051   $38.05   $38.05   $38.10  
  Purchase #4 $74.34   3.255%   $76.7598   $76.76   $76.75   $76.80  
  Purchase #5 $176.40   12.316%   $198.1254   $198.13   $198.15   $198.10  
  Purchase #6 $246.85   13.714%   $280.703   $280.70   $280.70   $280.70  
  Purchase #7 $31.81   11.512%   $35.472   $35.47   $35.45   $35.50  
  7 purchase totals = $887.31       $980.7388   $980.74   $980.75   $980.80