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 $26.57   10.113%   $29.257   $29.26   $29.25   $29.30  
  Purchase #2 $30.81   10.859%   $34.1557   $34.16   $34.15   $34.20  
  Purchase #3 $183.57   12.174%   $205.9178   $205.92   $205.90   $205.90  
  Purchase #4 $133.43   7.569%   $143.5293   $143.53   $143.55   $143.50  
  Purchase #5 $181.68   9.139%   $198.2837   $198.28   $198.30   $198.30  
  Purchase #6 $213.78   10.183%   $235.5492   $235.55   $235.55   $235.50  
  Purchase #7 $221.34   6.850%   $236.5018   $236.50   $236.50   $236.50  
  7 purchase totals = $991.18       $1,083.1945   $1,083.20   $1,083.20   $1,083.20