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 $246.50   10.231%   $271.7194   $271.72   $271.70   $271.70  
  Purchase #2 $197.61   11.664%   $220.6592   $220.66   $220.65   $220.70  
  Purchase #3 $41.69   7.261%   $44.7171   $44.72   $44.70   $44.70  
  Purchase #4 $159.37   12.545%   $179.363   $179.36   $179.35   $179.40  
  Purchase #5 $164.63   10.623%   $182.1186   $182.12   $182.10   $182.10  
  Purchase #6 $175.48   8.491%   $190.38   $190.38   $190.40   $190.40  
  Purchase #7 $190.42   9.216%   $207.9691   $207.97   $207.95   $208.00  
  7 purchase totals = $1,175.70       $1,296.9264   $1,296.93   $1,296.85   $1,297.00