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 $59.91   11.821%   $66.992   $66.99   $67.00   $67.00  
  Purchase #2 $101.90   11.874%   $113.9996   $114.00   $114.00   $114.00  
  Purchase #3 $156.31   7.333%   $167.7722   $167.77   $167.75   $167.80  
  Purchase #4 $235.75   7.108%   $252.5071   $252.51   $252.50   $252.50  
  Purchase #5 $173.49   7.725%   $186.8921   $186.89   $186.90   $186.90  
  Purchase #6 $235.84   9.195%   $257.5255   $257.53   $257.55   $257.50  
  Purchase #7 $228.38   11.324%   $254.2418   $254.24   $254.25   $254.20  
  7 purchase totals = $1,191.58       $1,299.9303   $1,299.93   $1,299.95   $1,299.90