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 $245.71   6.611%   $261.9539   $261.95   $261.95   $262.00  
  Purchase #2 $107.62   4.803%   $112.789   $112.79   $112.80   $112.80  
  Purchase #3 $246.84   6.863%   $263.7806   $263.78   $263.80   $263.80  
  Purchase #4 $196.50   7.409%   $211.0587   $211.06   $211.05   $211.10  
  Purchase #5 $83.25   11.717%   $93.0044   $93.00   $93.00   $93.00  
  Purchase #6 $27.72   9.866%   $30.4549   $30.45   $30.45   $30.50  
  Purchase #7 $29.57   12.361%   $33.2251   $33.23   $33.25   $33.20  
  7 purchase totals = $937.21       $1,006.2666   $1,006.26   $1,006.30   $1,006.40