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 $226.85   9.746%   $248.9588   $248.96   $248.95   $249.00  
  Purchase #2 $129.73   10.301%   $143.0935   $143.09   $143.10   $143.10  
  Purchase #3 $217.89   11.487%   $242.919   $242.92   $242.90   $242.90  
  Purchase #4 $184.50   5.109%   $193.9261   $193.93   $193.95   $193.90  
  Purchase #5 $31.55   9.694%   $34.6085   $34.61   $34.60   $34.60  
  Purchase #6 $43.25   9.348%   $47.293   $47.29   $47.30   $47.30  
  Purchase #7 $189.68   11.712%   $211.8953   $211.90   $211.90   $211.90  
  7 purchase totals = $1,023.45       $1,122.6942   $1,122.70   $1,122.70   $1,122.70