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 $229.65   8.265%   $248.6306   $248.63   $248.65   $248.60  
  Purchase #2 $94.67   13.690%   $107.6303   $107.63   $107.65   $107.60  
  Purchase #3 $123.33   8.715%   $134.0782   $134.08   $134.10   $134.10  
  Purchase #4 $22.38   6.143%   $23.7548   $23.75   $23.75   $23.80  
  Purchase #5 $51.97   11.477%   $57.9346   $57.93   $57.95   $57.90  
  Purchase #6 $63.84   8.409%   $69.2083   $69.21   $69.20   $69.20  
  Purchase #7 $247.57   4.524%   $258.7701   $258.77   $258.75   $258.80  
  7 purchase totals = $833.41       $900.0069   $900.00   $900.05   $900.00