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 $81.48   13.839%   $92.756   $92.76   $92.75   $92.80  
  Purchase #2 $227.78   12.500%   $256.2525   $256.25   $256.25   $256.30  
  Purchase #3 $181.70   6.102%   $192.7873   $192.79   $192.80   $192.80  
  Purchase #4 $36.72   11.618%   $40.9861   $40.99   $41.00   $41.00  
  Purchase #5 $208.35   11.419%   $232.1415   $232.14   $232.15   $232.10  
  Purchase #6 $208.38   12.524%   $234.4775   $234.48   $234.50   $234.50  
  Purchase #7 $30.30   13.236%   $34.3105   $34.31   $34.30   $34.30  
  7 purchase totals = $974.71       $1,083.7114   $1,083.72   $1,083.75   $1,083.80