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 $85.27   13.247%   $96.5657   $96.57   $96.55   $96.60  
  Purchase #2 $231.82   12.688%   $261.2333   $261.23   $261.25   $261.20  
  Purchase #3 $209.40   8.263%   $226.7027   $226.70   $226.70   $226.70  
  Purchase #4 $226.73   8.611%   $246.2537   $246.25   $246.25   $246.30  
  Purchase #5 $85.75   11.260%   $95.4055   $95.41   $95.40   $95.40  
  Purchase #6 $78.55   6.340%   $83.5301   $83.53   $83.55   $83.50  
  Purchase #7 $53.75   4.156%   $55.9839   $55.98   $56.00   $56.00  
  7 purchase totals = $971.27       $1,065.6749   $1,065.67   $1,065.70   $1,065.70