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 $76.50   10.105%   $84.2303   $84.23   $84.25   $84.20  
  Purchase #2 $115.91   7.695%   $124.8293   $124.83   $124.85   $124.80  
  Purchase #3 $44.61   3.648%   $46.2374   $46.24   $46.25   $46.20  
  Purchase #4 $59.76   12.500%   $67.23   $67.23   $67.25   $67.20  
  Purchase #5 $247.90   5.476%   $261.475   $261.48   $261.50   $261.50  
  Purchase #6 $217.91   7.411%   $234.0593   $234.06   $234.05   $234.10  
  Purchase #7 $88.96   5.724%   $94.0521   $94.05   $94.05   $94.10  
  7 purchase totals = $851.55       $912.1134   $912.12   $912.20   $912.10