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 $59.66   5.859%   $63.1555   $63.16   $63.15   $63.20  
  Purchase #2 $105.54   13.648%   $119.9441   $119.94   $119.95   $119.90  
  Purchase #3 $227.95   3.397%   $235.6935   $235.69   $235.70   $235.70  
  Purchase #4 $21.98   3.309%   $22.7073   $22.71   $22.70   $22.70  
  Purchase #5 $250.93   7.764%   $270.4122   $270.41   $270.40   $270.40  
  Purchase #6 $205.69   6.498%   $219.0557   $219.06   $219.05   $219.10  
  Purchase #7 $127.54   13.120%   $144.2732   $144.27   $144.25   $144.30  
  7 purchase totals = $999.29       $1,075.2415   $1,075.24   $1,075.20   $1,075.30