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 $234.57   11.392%   $261.2922   $261.29   $261.30   $261.30  
  Purchase #2 $164.64   10.151%   $181.3526   $181.35   $181.35   $181.40  
  Purchase #3 $107.79   4.789%   $112.9521   $112.95   $112.95   $113.00  
  Purchase #4 $191.32   9.262%   $209.0401   $209.04   $209.05   $209.00  
  Purchase #5 $215.81   8.430%   $234.0028   $234.00   $234.00   $234.00  
  Purchase #6 $148.97   3.202%   $153.74   $153.74   $153.75   $153.70  
  Purchase #7 $183.38   4.328%   $191.3167   $191.32   $191.30   $191.30  
  7 purchase totals = $1,246.48       $1,343.6965   $1,343.69   $1,343.70   $1,343.70