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 $60.79   5.699%   $64.2544   $64.25   $64.25   $64.30  
  Purchase #2 $246.41   3.767%   $255.6923   $255.69   $255.70   $255.70  
  Purchase #3 $114.45   3.166%   $118.0735   $118.07   $118.05   $118.10  
  Purchase #4 $17.81   8.357%   $19.2984   $19.30   $19.30   $19.30  
  Purchase #5 $79.51   6.270%   $84.4953   $84.50   $84.50   $84.50  
  Purchase #6 $21.83   3.801%   $22.6598   $22.66   $22.65   $22.70  
  Purchase #7 $57.88   5.844%   $61.2625   $61.26   $61.25   $61.30  
  7 purchase totals = $598.68       $625.7362   $625.73   $625.70   $625.90