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 $248.95   4.536%   $260.2424   $260.24   $260.25   $260.20  
  Purchase #2 $5.63   8.351%   $6.1002   $6.10   $6.10   $6.10  
  Purchase #3 $228.45   3.769%   $237.0603   $237.06   $237.05   $237.10  
  Purchase #4 $117.25   11.443%   $130.6669   $130.67   $130.65   $130.70  
  Purchase #5 $38.41   13.238%   $43.4947   $43.49   $43.50   $43.50  
  Purchase #6 $135.92   11.432%   $151.4584   $151.46   $151.45   $151.50  
  Purchase #7 $163.38   11.249%   $181.7586   $181.76   $181.75   $181.80  
  7 purchase totals = $937.99       $1,010.7815   $1,010.78   $1,010.75   $1,010.90