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 $244.74   11.786%   $273.5851   $273.59   $273.60   $273.60  
  Purchase #2 $150.66   4.735%   $157.7938   $157.79   $157.80   $157.80  
  Purchase #3 $245.99   5.442%   $259.3768   $259.38   $259.40   $259.40  
  Purchase #4 $27.92   10.641%   $30.891   $30.89   $30.90   $30.90  
  Purchase #5 $183.45   7.628%   $197.4436   $197.44   $197.45   $197.40  
  Purchase #6 $119.87   12.273%   $134.5816   $134.58   $134.60   $134.60  
  Purchase #7 $108.72   13.270%   $123.1471   $123.15   $123.15   $123.10  
  7 purchase totals = $1,081.35       $1,176.8190   $1,176.82   $1,176.90   $1,176.80