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 $57.72   8.258%   $62.4865   $62.49   $62.50   $62.50  
  Purchase #2 $226.36   3.295%   $233.8186   $233.82   $233.80   $233.80  
  Purchase #3 $113.64   6.215%   $120.7027   $120.70   $120.70   $120.70  
  Purchase #4 $236.90   11.645%   $264.487   $264.49   $264.50   $264.50  
  Purchase #5 $27.77   13.797%   $31.6014   $31.60   $31.60   $31.60  
  Purchase #6 $130.94   8.448%   $142.0018   $142.00   $142.00   $142.00  
  Purchase #7 $242.38   4.271%   $252.732   $252.73   $252.75   $252.70  
  7 purchase totals = $1,035.71       $1,107.8300   $1,107.83   $1,107.85   $1,107.80