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 $96.77   13.248%   $109.5901   $109.59   $109.60   $109.60  
  Purchase #2 $124.84   9.508%   $136.7098   $136.71   $136.70   $136.70  
  Purchase #3 $68.48   12.773%   $77.227   $77.23   $77.25   $77.20  
  Purchase #4 $79.87   3.250%   $82.4658   $82.47   $82.45   $82.50  
  Purchase #5 $122.62   6.563%   $130.6676   $130.67   $130.65   $130.70  
  Purchase #6 $198.44   3.721%   $205.824   $205.82   $205.80   $205.80  
  Purchase #7 $191.65   7.339%   $205.7152   $205.72   $205.70   $205.70  
  7 purchase totals = $882.67       $948.1995   $948.21   $948.15   $948.20