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 $209.40   12.696%   $235.9854   $235.99   $236.00   $236.00  
  Purchase #2 $233.90   12.421%   $262.9527   $262.95   $262.95   $263.00  
  Purchase #3 $209.58   12.361%   $235.4862   $235.49   $235.50   $235.50  
  Purchase #4 $73.27   5.315%   $77.1643   $77.16   $77.15   $77.20  
  Purchase #5 $164.86   11.552%   $183.9046   $183.90   $183.90   $183.90  
  Purchase #6 $187.73   13.639%   $213.3345   $213.33   $213.35   $213.30  
  Purchase #7 $67.26   13.309%   $76.2116   $76.21   $76.20   $76.20  
  7 purchase totals = $1,146.00       $1,285.0393   $1,285.03   $1,285.05   $1,285.10