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 $56.58   11.322%   $62.986   $62.99   $63.00   $63.00  
  Purchase #2 $186.45   11.832%   $208.5108   $208.51   $208.50   $208.50  
  Purchase #3 $120.56   4.242%   $125.6742   $125.67   $125.65   $125.70  
  Purchase #4 $26.41   3.198%   $27.2546   $27.25   $27.25   $27.30  
  Purchase #5 $20.89   7.422%   $22.4405   $22.44   $22.45   $22.40  
  Purchase #6 $28.66   7.661%   $30.8556   $30.86   $30.85   $30.90  
  Purchase #7 $52.63   4.306%   $54.8962   $54.90   $54.90   $54.90  
  7 purchase totals = $492.18       $532.6179   $532.62   $532.60   $532.70