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 $42.47   11.755%   $47.4623   $47.46   $47.45   $47.50  
  Purchase #2 $136.36   12.334%   $153.1786   $153.18   $153.20   $153.20  
  Purchase #3 $162.47   12.653%   $183.0273   $183.03   $183.05   $183.00  
  Purchase #4 $212.82   12.330%   $239.0607   $239.06   $239.05   $239.10  
  Purchase #5 $204.63   9.576%   $224.2254   $224.23   $224.25   $224.20  
  Purchase #6 $8.92   4.686%   $9.338   $9.34   $9.35   $9.30  
  Purchase #7 $97.87   9.538%   $107.2048   $107.20   $107.20   $107.20  
  7 purchase totals = $865.54       $963.4971   $963.50   $963.55   $963.50