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 $61.71   7.629%   $66.4179   $66.42   $66.40   $66.40  
  Purchase #2 $134.72   4.848%   $141.2512   $141.25   $141.25   $141.30  
  Purchase #3 $182.54   13.613%   $207.3892   $207.39   $207.40   $207.40  
  Purchase #4 $223.99   4.672%   $234.4548   $234.45   $234.45   $234.50  
  Purchase #5 $58.67   8.649%   $63.7444   $63.74   $63.75   $63.70  
  Purchase #6 $215.30   9.708%   $236.2013   $236.20   $236.20   $236.20  
  Purchase #7 $167.97   10.591%   $185.7597   $185.76   $185.75   $185.80  
  7 purchase totals = $1,044.90       $1,135.2185   $1,135.21   $1,135.20   $1,135.30