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 $93.45   5.871%   $98.9364   $98.94   $98.95   $98.90  
  Purchase #2 $85.45   7.291%   $91.6802   $91.68   $91.70   $91.70  
  Purchase #3 $164.56   5.292%   $173.2685   $173.27   $173.25   $173.30  
  Purchase #4 $70.60   8.116%   $76.3299   $76.33   $76.35   $76.30  
  Purchase #5 $198.65   7.776%   $214.097   $214.10   $214.10   $214.10  
  Purchase #6 $133.90   4.809%   $140.3393   $140.34   $140.35   $140.30  
  Purchase #7 $178.31   13.434%   $202.2642   $202.26   $202.25   $202.30  
  7 purchase totals = $924.92       $996.9155   $996.92   $996.95   $996.90