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 $229.70   12.608%   $258.6606   $258.66   $258.65   $258.70  
  Purchase #2 $68.37   11.364%   $76.1396   $76.14   $76.15   $76.10  
  Purchase #3 $94.29   4.213%   $98.2624   $98.26   $98.25   $98.30  
  Purchase #4 $90.63   10.564%   $100.2042   $100.20   $100.20   $100.20  
  Purchase #5 $93.94   8.451%   $101.8789   $101.88   $101.90   $101.90  
  Purchase #6 $122.62   10.259%   $135.1996   $135.20   $135.20   $135.20  
  Purchase #7 $222.88   8.220%   $241.2007   $241.20   $241.20   $241.20  
  7 purchase totals = $922.43       $1,011.5460   $1,011.54   $1,011.55   $1,011.60