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 $245.84   6.435%   $261.6598   $261.66   $261.65   $261.70  
  Purchase #2 $185.78   8.619%   $201.7924   $201.79   $201.80   $201.80  
  Purchase #3 $243.60   11.338%   $271.2194   $271.22   $271.20   $271.20  
  Purchase #4 $176.44   10.556%   $195.065   $195.07   $195.05   $195.10  
  Purchase #5 $44.29   5.460%   $46.7082   $46.71   $46.70   $46.70  
  Purchase #6 $23.78   3.153%   $24.5298   $24.53   $24.55   $24.50  
  Purchase #7 $119.98   8.506%   $130.1855   $130.19   $130.20   $130.20  
  7 purchase totals = $1,039.71       $1,131.1601   $1,131.17   $1,131.15   $1,131.20