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 $186.48   11.568%   $208.052   $208.05   $208.05   $208.10  
  Purchase #2 $8.84   12.564%   $9.9507   $9.95   $9.95   $10.00  
  Purchase #3 $115.35   10.696%   $127.6878   $127.69   $127.70   $127.70  
  Purchase #4 $175.67   8.185%   $190.0486   $190.05   $190.05   $190.00  
  Purchase #5 $230.33   13.392%   $261.1758   $261.18   $261.20   $261.20  
  Purchase #6 $83.89   11.503%   $93.5399   $93.54   $93.55   $93.50  
  Purchase #7 $75.34   5.216%   $79.2697   $79.27   $79.25   $79.30  
  7 purchase totals = $875.90       $969.7245   $969.73   $969.75   $969.80