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 $234.61   11.599%   $261.8224   $261.82   $261.80   $261.80  
  Purchase #2 $90.98   5.254%   $95.7601   $95.76   $95.75   $95.80  
  Purchase #3 $201.49   13.342%   $228.3728   $228.37   $228.35   $228.40  
  Purchase #4 $5.57   3.314%   $5.7546   $5.75   $5.75   $5.80  
  Purchase #5 $107.92   3.570%   $111.7727   $111.77   $111.75   $111.80  
  Purchase #6 $57.40   8.200%   $62.1068   $62.11   $62.10   $62.10  
  Purchase #7 $9.86   13.786%   $11.2193   $11.22   $11.20   $11.20  
  7 purchase totals = $707.83       $776.8087   $776.80   $776.70   $776.90