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 $228.39   3.299%   $235.9246   $235.92   $235.90   $235.90  
  Purchase #2 $57.45   12.492%   $64.6267   $64.63   $64.65   $64.60  
  Purchase #3 $187.81   5.423%   $197.9949   $197.99   $198.00   $198.00  
  Purchase #4 $101.34   12.488%   $113.9953   $114.00   $114.00   $114.00  
  Purchase #5 $25.70   4.815%   $26.9375   $26.94   $26.95   $26.90  
  Purchase #6 $159.79   6.391%   $170.0022   $170.00   $170.00   $170.00  
  Purchase #7 $191.72   13.282%   $217.1843   $217.18   $217.20   $217.20  
  7 purchase totals = $952.20       $1,026.6655   $1,026.66   $1,026.70   $1,026.60