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 $241.85   10.757%   $267.8658   $267.87   $267.85   $267.90  
  Purchase #2 $224.71   4.234%   $234.2242   $234.22   $234.20   $234.20  
  Purchase #3 $221.30   8.762%   $240.6903   $240.69   $240.70   $240.70  
  Purchase #4 $161.31   6.232%   $171.3628   $171.36   $171.35   $171.40  
  Purchase #5 $176.80   6.856%   $188.9214   $188.92   $188.90   $188.90  
  Purchase #6 $158.72   10.181%   $174.8793   $174.88   $174.90   $174.90  
  Purchase #7 $110.37   4.122%   $114.9195   $114.92   $114.90   $114.90  
  7 purchase totals = $1,295.06       $1,392.8633   $1,392.86   $1,392.80   $1,392.90