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 $102.87   11.426%   $114.6239   $114.62   $114.60   $114.60  
  Purchase #2 $174.42   3.149%   $179.9125   $179.91   $179.90   $179.90  
  Purchase #3 $146.52   12.554%   $164.9141   $164.91   $164.90   $164.90  
  Purchase #4 $79.58   11.455%   $88.6959   $88.70   $88.70   $88.70  
  Purchase #5 $151.43   7.395%   $162.6282   $162.63   $162.65   $162.60  
  Purchase #6 $243.53   5.781%   $257.6085   $257.61   $257.60   $257.60  
  Purchase #7 $144.40   4.528%   $150.9384   $150.94   $150.95   $150.90  
  7 purchase totals = $1,042.75       $1,119.3215   $1,119.32   $1,119.30   $1,119.20