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 $164.27   11.826%   $183.6966   $183.70   $183.70   $183.70  
  Purchase #2 $63.88   5.203%   $67.2037   $67.20   $67.20   $67.20  
  Purchase #3 $77.95   6.128%   $82.7268   $82.73   $82.75   $82.70  
  Purchase #4 $228.25   9.211%   $249.2741   $249.27   $249.25   $249.30  
  Purchase #5 $52.35   13.357%   $59.3424   $59.34   $59.35   $59.30  
  Purchase #6 $42.61   13.599%   $48.4045   $48.40   $48.40   $48.40  
  Purchase #7 $231.76   11.137%   $257.5711   $257.57   $257.55   $257.60  
  7 purchase totals = $861.07       $948.2192   $948.21   $948.20   $948.20