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 $208.87   13.549%   $237.1698   $237.17   $237.15   $237.20  
  Purchase #2 $19.53   11.709%   $21.8168   $21.82   $21.80   $21.80  
  Purchase #3 $242.96   3.228%   $250.8027   $250.80   $250.80   $250.80  
  Purchase #4 $126.82   3.253%   $130.9455   $130.95   $130.95   $130.90  
  Purchase #5 $104.25   8.790%   $113.4136   $113.41   $113.40   $113.40  
  Purchase #6 $248.59   8.625%   $270.0309   $270.03   $270.05   $270.00  
  Purchase #7 $22.40   10.814%   $24.8223   $24.82   $24.80   $24.80  
  7 purchase totals = $973.42       $1,049.0016   $1,049.00   $1,048.95   $1,048.90