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 $236.58   10.132%   $260.5503   $260.55   $260.55   $260.60  
  Purchase #2 $239.50   8.327%   $259.4432   $259.44   $259.45   $259.40  
  Purchase #3 $129.69   9.271%   $141.7136   $141.71   $141.70   $141.70  
  Purchase #4 $248.87   9.399%   $272.2613   $272.26   $272.25   $272.30  
  Purchase #5 $87.47   8.517%   $94.9198   $94.92   $94.90   $94.90  
  Purchase #6 $6.34   5.388%   $6.6816   $6.68   $6.70   $6.70  
  Purchase #7 $23.79   10.680%   $26.3308   $26.33   $26.35   $26.30  
  7 purchase totals = $972.24       $1,061.9006   $1,061.89   $1,061.90   $1,061.90