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 $211.76   6.226%   $224.9442   $224.94   $224.95   $224.90  
  Purchase #2 $49.60   13.572%   $56.3317   $56.33   $56.35   $56.30  
  Purchase #3 $146.55   4.618%   $153.3177   $153.32   $153.30   $153.30  
  Purchase #4 $89.97   3.443%   $93.0677   $93.07   $93.05   $93.10  
  Purchase #5 $101.99   10.136%   $112.3277   $112.33   $112.35   $112.30  
  Purchase #6 $146.32   11.587%   $163.2741   $163.27   $163.25   $163.30  
  Purchase #7 $104.93   9.336%   $114.7263   $114.73   $114.75   $114.70  
  7 purchase totals = $851.12       $917.9894   $917.99   $918.00   $917.90