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 $227.97   10.661%   $252.2739   $252.27   $252.25   $252.30  
  Purchase #2 $166.70   13.762%   $189.6413   $189.64   $189.65   $189.60  
  Purchase #3 $137.92   4.867%   $144.6326   $144.63   $144.65   $144.60  
  Purchase #4 $139.71   10.671%   $154.6185   $154.62   $154.60   $154.60  
  Purchase #5 $51.38   6.379%   $54.6575   $54.66   $54.65   $54.70  
  Purchase #6 $97.44   4.668%   $101.9885   $101.99   $102.00   $102.00  
  Purchase #7 $103.32   11.116%   $114.8051   $114.81   $114.80   $114.80  
  7 purchase totals = $924.44       $1,012.6174   $1,012.62   $1,012.60   $1,012.60