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 $23.39   8.388%   $25.352   $25.35   $25.35   $25.40  
  Purchase #2 $235.32   6.519%   $250.6605   $250.66   $250.65   $250.70  
  Purchase #3 $33.63   9.274%   $36.7488   $36.75   $36.75   $36.70  
  Purchase #4 $215.85   12.491%   $242.8118   $242.81   $242.80   $242.80  
  Purchase #5 $205.76   10.649%   $227.6714   $227.67   $227.65   $227.70  
  Purchase #6 $17.91   10.599%   $19.8083   $19.81   $19.80   $19.80  
  Purchase #7 $96.40   6.168%   $102.346   $102.35   $102.35   $102.30  
  7 purchase totals = $828.26       $905.3988   $905.40   $905.35   $905.40