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 $61.76   6.828%   $65.977   $65.98   $66.00   $66.00  
  Purchase #2 $111.64   12.792%   $125.921   $125.92   $125.90   $125.90  
  Purchase #3 $174.38   13.473%   $197.8742   $197.87   $197.85   $197.90  
  Purchase #4 $126.63   11.865%   $141.6546   $141.65   $141.65   $141.70  
  Purchase #5 $248.71   10.229%   $274.1505   $274.15   $274.15   $274.20  
  Purchase #6 $124.55   13.604%   $141.4938   $141.49   $141.50   $141.50  
  Purchase #7 $14.37   8.712%   $15.6219   $15.62   $15.60   $15.60  
  7 purchase totals = $862.04       $962.6930   $962.68   $962.65   $962.80