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 $118.69   13.128%   $134.2716   $134.27   $134.25   $134.30  
  Purchase #2 $166.76   13.478%   $189.2359   $189.24   $189.25   $189.20  
  Purchase #3 $165.27   6.706%   $176.353   $176.35   $176.35   $176.40  
  Purchase #4 $233.46   3.830%   $242.4015   $242.40   $242.40   $242.40  
  Purchase #5 $206.72   10.707%   $228.8535   $228.85   $228.85   $228.90  
  Purchase #6 $27.57   9.359%   $30.1503   $30.15   $30.15   $30.20  
  Purchase #7 $96.95   8.509%   $105.1995   $105.20   $105.20   $105.20  
  7 purchase totals = $1,015.42       $1,106.4653   $1,106.46   $1,106.45   $1,106.60