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 $58.95   5.826%   $62.3844   $62.38   $62.40   $62.40  
  Purchase #2 $98.28   4.589%   $102.7901   $102.79   $102.80   $102.80  
  Purchase #3 $242.99   4.403%   $253.6888   $253.69   $253.70   $253.70  
  Purchase #4 $100.66   8.432%   $109.1477   $109.15   $109.15   $109.10  
  Purchase #5 $68.51   6.398%   $72.8933   $72.89   $72.90   $72.90  
  Purchase #6 $206.31   8.576%   $224.0031   $224.00   $224.00   $224.00  
  Purchase #7 $127.35   10.564%   $140.8033   $140.80   $140.80   $140.80  
  7 purchase totals = $903.05       $965.7107   $965.70   $965.75   $965.70