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 $54.92   10.353%   $60.6059   $60.61   $60.60   $60.60  
  Purchase #2 $243.53   12.360%   $273.6303   $273.63   $273.65   $273.60  
  Purchase #3 $240.87   4.799%   $252.4294   $252.43   $252.45   $252.40  
  Purchase #4 $78.87   3.756%   $81.8324   $81.83   $81.85   $81.80  
  Purchase #5 $50.25   8.772%   $54.6579   $54.66   $54.65   $54.70  
  Purchase #6 $166.38   11.725%   $185.8881   $185.89   $185.90   $185.90  
  Purchase #7 $93.42   12.396%   $105.0003   $105.00   $105.00   $105.00  
  7 purchase totals = $928.24       $1,014.0443   $1,014.05   $1,014.10   $1,014.00