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 $239.83   9.463%   $262.5251   $262.53   $262.55   $262.50  
  Purchase #2 $12.95   9.865%   $14.2275   $14.23   $14.25   $14.20  
  Purchase #3 $77.99   7.544%   $83.8736   $83.87   $83.85   $83.90  
  Purchase #4 $33.61   9.150%   $36.6853   $36.69   $36.70   $36.70  
  Purchase #5 $207.65   9.792%   $227.9831   $227.98   $228.00   $228.00  
  Purchase #6 $193.54   13.206%   $219.0989   $219.10   $219.10   $219.10  
  Purchase #7 $246.41   6.293%   $261.9166   $261.92   $261.90   $261.90  
  7 purchase totals = $1,011.98       $1,106.3101   $1,106.32   $1,106.35   $1,106.30