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 $92.75   13.822%   $105.5699   $105.57   $105.55   $105.60  
  Purchase #2 $181.90   11.311%   $202.4747   $202.47   $202.45   $202.50  
  Purchase #3 $98.34   6.154%   $104.3918   $104.39   $104.40   $104.40  
  Purchase #4 $114.50   8.341%   $124.0504   $124.05   $124.05   $124.10  
  Purchase #5 $44.25   13.807%   $50.3596   $50.36   $50.35   $50.40  
  Purchase #6 $218.80   10.831%   $242.4982   $242.50   $242.50   $242.50  
  Purchase #7 $49.27   10.596%   $54.4906   $54.49   $54.50   $54.50  
  7 purchase totals = $799.81       $883.8352   $883.83   $883.80   $884.00