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 $93.28   12.338%   $104.7889   $104.79   $104.80   $104.80  
  Purchase #2 $247.71   4.821%   $259.6521   $259.65   $259.65   $259.70  
  Purchase #3 $124.68   13.479%   $141.4856   $141.49   $141.50   $141.50  
  Purchase #4 $181.60   12.425%   $204.1638   $204.16   $204.15   $204.20  
  Purchase #5 $157.88   8.630%   $171.505   $171.51   $171.50   $171.50  
  Purchase #6 $244.67   8.412%   $265.2516   $265.25   $265.25   $265.30  
  Purchase #7 $101.54   12.646%   $114.3807   $114.38   $114.40   $114.40  
  7 purchase totals = $1,151.36       $1,261.2277   $1,261.23   $1,261.25   $1,261.40