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 $182.25   12.243%   $204.5629   $204.56   $204.55   $204.60  
  Purchase #2 $94.72   4.451%   $98.936   $98.94   $98.95   $98.90  
  Purchase #3 $138.72   13.551%   $157.5179   $157.52   $157.50   $157.50  
  Purchase #4 $70.41   6.153%   $74.7423   $74.74   $74.75   $74.70  
  Purchase #5 $89.26   10.518%   $98.6484   $98.65   $98.65   $98.60  
  Purchase #6 $100.95   9.214%   $110.2515   $110.25   $110.25   $110.30  
  Purchase #7 $186.81   11.833%   $208.9152   $208.92   $208.90   $208.90  
  7 purchase totals = $863.12       $953.5742   $953.58   $953.55   $953.50