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 $32.25   8.646%   $35.0383   $35.04   $35.05   $35.00  
  Purchase #2 $213.81   12.547%   $240.6367   $240.64   $240.65   $240.60  
  Purchase #3 $5.96   11.685%   $6.6564   $6.66   $6.65   $6.70  
  Purchase #4 $212.99   7.739%   $229.4733   $229.47   $229.45   $229.50  
  Purchase #5 $74.80   9.264%   $81.7295   $81.73   $81.75   $81.70  
  Purchase #6 $152.56   3.309%   $157.6082   $157.61   $157.60   $157.60  
  Purchase #7 $82.54   3.714%   $85.6055   $85.61   $85.60   $85.60  
  7 purchase totals = $774.91       $836.7479   $836.76   $836.75   $836.70