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 $52.61   9.371%   $57.5401   $57.54   $57.55   $57.50  
  Purchase #2 $94.79   13.685%   $107.762   $107.76   $107.75   $107.80  
  Purchase #3 $168.89   4.180%   $175.9496   $175.95   $175.95   $175.90  
  Purchase #4 $243.54   7.524%   $261.8639   $261.86   $261.85   $261.90  
  Purchase #5 $162.89   12.753%   $183.6634   $183.66   $183.65   $183.70  
  Purchase #6 $67.84   9.531%   $74.3058   $74.31   $74.30   $74.30  
  Purchase #7 $6.86   11.221%   $7.6298   $7.63   $7.65   $7.60  
  7 purchase totals = $797.42       $868.7146   $868.71   $868.70   $868.70