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 $237.67   4.747%   $248.9522   $248.95   $248.95   $249.00  
  Purchase #2 $198.99   3.143%   $205.2443   $205.24   $205.25   $205.20  
  Purchase #3 $70.42   7.227%   $75.5093   $75.51   $75.50   $75.50  
  Purchase #4 $107.89   13.120%   $122.0452   $122.05   $122.05   $122.00  
  Purchase #5 $212.91   12.397%   $239.3045   $239.30   $239.30   $239.30  
  Purchase #6 $134.67   11.307%   $149.8971   $149.90   $149.90   $149.90  
  Purchase #7 $51.86   8.856%   $56.4527   $56.45   $56.45   $56.50  
  7 purchase totals = $1,014.41       $1,097.4053   $1,097.40   $1,097.40   $1,097.40