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 $202.93   11.380%   $226.0234   $226.02   $226.00   $226.00  
  Purchase #2 $191.57   5.664%   $202.4205   $202.42   $202.40   $202.40  
  Purchase #3 $27.76   11.597%   $30.9793   $30.98   $31.00   $31.00  
  Purchase #4 $107.50   6.552%   $114.5434   $114.54   $114.55   $114.50  
  Purchase #5 $36.74   12.157%   $41.2065   $41.21   $41.20   $41.20  
  Purchase #6 $78.91   12.304%   $88.6191   $88.62   $88.60   $88.60  
  Purchase #7 $200.76   5.235%   $211.2698   $211.27   $211.25   $211.30  
  7 purchase totals = $846.17       $915.0620   $915.06   $915.00   $915.00