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 $239.55   10.621%   $264.9926   $264.99   $265.00   $265.00  
  Purchase #2 $101.29   11.339%   $112.7753   $112.78   $112.80   $112.80  
  Purchase #3 $118.60   12.270%   $133.1522   $133.15   $133.15   $133.20  
  Purchase #4 $213.69   13.540%   $242.6236   $242.62   $242.60   $242.60  
  Purchase #5 $196.29   5.397%   $206.8838   $206.88   $206.90   $206.90  
  Purchase #6 $82.34   11.766%   $92.0281   $92.03   $92.05   $92.00  
  Purchase #7 $188.66   10.498%   $208.4655   $208.47   $208.45   $208.50  
  7 purchase totals = $1,140.42       $1,260.9211   $1,260.92   $1,260.95   $1,261.00