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 $226.79   9.681%   $248.7455   $248.75   $248.75   $248.70  
  Purchase #2 $235.26   11.518%   $262.3572   $262.36   $262.35   $262.40  
  Purchase #3 $23.69   8.725%   $25.757   $25.76   $25.75   $25.80  
  Purchase #4 $164.35   3.452%   $170.0234   $170.02   $170.00   $170.00  
  Purchase #5 $68.32   12.725%   $77.0137   $77.01   $77.00   $77.00  
  Purchase #6 $69.42   8.273%   $75.1631   $75.16   $75.15   $75.20  
  Purchase #7 $128.88   11.289%   $143.4293   $143.43   $143.45   $143.40  
  7 purchase totals = $916.71       $1,002.4892   $1,002.49   $1,002.45   $1,002.50