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 $183.97   11.735%   $205.5589   $205.56   $205.55   $205.60  
  Purchase #2 $141.69   9.177%   $154.6929   $154.69   $154.70   $154.70  
  Purchase #3 $141.89   4.443%   $148.1942   $148.19   $148.20   $148.20  
  Purchase #4 $57.39   10.799%   $63.5875   $63.59   $63.60   $63.60  
  Purchase #5 $166.93   4.182%   $173.911   $173.91   $173.90   $173.90  
  Purchase #6 $46.25   4.560%   $48.359   $48.36   $48.35   $48.40  
  Purchase #7 $131.56   4.317%   $137.2394   $137.24   $137.25   $137.20  
  7 purchase totals = $869.68       $931.5429   $931.54   $931.55   $931.60