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 $238.65   4.119%   $248.48   $248.48   $248.50   $248.50  
  Purchase #2 $212.35   6.425%   $225.9935   $225.99   $226.00   $226.00  
  Purchase #3 $119.67   11.161%   $133.0264   $133.03   $133.05   $133.00  
  Purchase #4 $122.51   8.782%   $133.2688   $133.27   $133.25   $133.30  
  Purchase #5 $114.25   10.568%   $126.3239   $126.32   $126.30   $126.30  
  Purchase #6 $86.97   6.762%   $92.8509   $92.85   $92.85   $92.90  
  Purchase #7 $46.36   6.734%   $49.4819   $49.48   $49.50   $49.50  
  7 purchase totals = $940.76       $1,009.4254   $1,009.42   $1,009.45   $1,009.50