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 $52.26   5.757%   $55.2686   $55.27   $55.25   $55.30  
  Purchase #2 $162.69   7.741%   $175.2838   $175.28   $175.30   $175.30  
  Purchase #3 $114.31   8.746%   $124.3076   $124.31   $124.30   $124.30  
  Purchase #4 $226.94   4.102%   $236.2491   $236.25   $236.25   $236.20  
  Purchase #5 $149.66   5.756%   $158.2744   $158.27   $158.25   $158.30  
  Purchase #6 $23.58   4.664%   $24.6798   $24.68   $24.70   $24.70  
  Purchase #7 $135.87   11.533%   $151.5399   $151.54   $151.55   $151.50  
  7 purchase totals = $865.31       $925.6032   $925.60   $925.60   $925.60