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 $49.67   10.186%   $54.7294   $54.73   $54.75   $54.70  
  Purchase #2 $105.87   3.602%   $109.6834   $109.68   $109.70   $109.70  
  Purchase #3 $113.73   8.110%   $122.9535   $122.95   $122.95   $123.00  
  Purchase #4 $102.75   7.434%   $110.3884   $110.39   $110.40   $110.40  
  Purchase #5 $168.68   9.713%   $185.0639   $185.06   $185.05   $185.10  
  Purchase #6 $160.75   8.339%   $174.1549   $174.15   $174.15   $174.20  
  Purchase #7 $111.72   13.254%   $126.5274   $126.53   $126.55   $126.50  
  7 purchase totals = $813.17       $883.5009   $883.49   $883.55   $883.60