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 $62.96   12.145%   $70.6065   $70.61   $70.60   $70.60  
  Purchase #2 $183.60   13.818%   $208.9698   $208.97   $208.95   $209.00  
  Purchase #3 $196.64   5.478%   $207.4119   $207.41   $207.40   $207.40  
  Purchase #4 $137.66   6.415%   $146.4909   $146.49   $146.50   $146.50  
  Purchase #5 $153.39   12.442%   $172.4748   $172.47   $172.45   $172.50  
  Purchase #6 $235.92   5.643%   $249.233   $249.23   $249.25   $249.20  
  Purchase #7 $239.89   9.208%   $261.9791   $261.98   $262.00   $262.00  
  7 purchase totals = $1,210.06       $1,317.1660   $1,317.16   $1,317.15   $1,317.20