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 $87.56   9.367%   $95.7617   $95.76   $95.75   $95.80  
  Purchase #2 $137.76   3.685%   $142.8365   $142.84   $142.85   $142.80  
  Purchase #3 $143.75   9.392%   $157.251   $157.25   $157.25   $157.30  
  Purchase #4 $146.53   12.443%   $164.7627   $164.76   $164.75   $164.80  
  Purchase #5 $168.83   11.439%   $188.1425   $188.14   $188.15   $188.10  
  Purchase #6 $67.31   8.597%   $73.0966   $73.10   $73.10   $73.10  
  Purchase #7 $126.27   12.214%   $141.6926   $141.69   $141.70   $141.70  
  7 purchase totals = $878.01       $963.5436   $963.54   $963.55   $963.60