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 $223.91   13.328%   $253.7527   $253.75   $253.75   $253.80  
  Purchase #2 $167.86   8.744%   $182.5377   $182.54   $182.55   $182.50  
  Purchase #3 $111.50   13.870%   $126.9651   $126.97   $126.95   $127.00  
  Purchase #4 $113.27   12.389%   $127.303   $127.30   $127.30   $127.30  
  Purchase #5 $239.92   4.465%   $250.6324   $250.63   $250.65   $250.60  
  Purchase #6 $63.75   9.626%   $69.8866   $69.89   $69.90   $69.90  
  Purchase #7 $240.46   10.749%   $266.307   $266.31   $266.30   $266.30  
  7 purchase totals = $1,160.67       $1,277.3845   $1,277.39   $1,277.40   $1,277.40