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 $117.44   5.504%   $123.9039   $123.90   $123.90   $123.90  
  Purchase #2 $224.48   3.683%   $232.7476   $232.75   $232.75   $232.70  
  Purchase #3 $101.27   7.364%   $108.7275   $108.73   $108.75   $108.70  
  Purchase #4 $68.76   11.544%   $76.6977   $76.70   $76.70   $76.70  
  Purchase #5 $235.58   9.318%   $257.5313   $257.53   $257.55   $257.50  
  Purchase #6 $136.48   7.195%   $146.2997   $146.30   $146.30   $146.30  
  Purchase #7 $237.40   5.612%   $250.7229   $250.72   $250.70   $250.70  
  7 purchase totals = $1,121.41       $1,196.6306   $1,196.63   $1,196.65   $1,196.50