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 $113.59   8.804%   $123.5905   $123.59   $123.60   $123.60  
  Purchase #2 $246.85   4.290%   $257.4399   $257.44   $257.45   $257.40  
  Purchase #3 $24.62   9.210%   $26.8875   $26.89   $26.90   $26.90  
  Purchase #4 $66.49   9.241%   $72.6343   $72.63   $72.65   $72.60  
  Purchase #5 $153.37   11.577%   $171.1256   $171.13   $171.15   $171.10  
  Purchase #6 $69.28   10.565%   $76.5994   $76.60   $76.60   $76.60  
  Purchase #7 $27.57   12.105%   $30.9073   $30.91   $30.90   $30.90  
  7 purchase totals = $701.77       $759.1845   $759.19   $759.25   $759.10