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 $206.45   8.523%   $224.0457   $224.05   $224.05   $224.00  
  Purchase #2 $24.38   8.503%   $26.453   $26.45   $26.45   $26.50  
  Purchase #3 $96.64   13.209%   $109.4052   $109.41   $109.40   $109.40  
  Purchase #4 $228.59   6.163%   $242.678   $242.68   $242.70   $242.70  
  Purchase #5 $222.38   3.822%   $230.8794   $230.88   $230.90   $230.90  
  Purchase #6 $82.31   9.127%   $89.8224   $89.82   $89.80   $89.80  
  Purchase #7 $60.71   3.177%   $62.6388   $62.64   $62.65   $62.60  
  7 purchase totals = $921.46       $985.9225   $985.93   $985.95   $985.90