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 $44.71   5.848%   $47.3246   $47.32   $47.30   $47.30  
  Purchase #2 $76.41   8.182%   $82.6619   $82.66   $82.65   $82.70  
  Purchase #3 $8.99   8.139%   $9.7217   $9.72   $9.70   $9.70  
  Purchase #4 $236.80   4.738%   $248.0196   $248.02   $248.00   $248.00  
  Purchase #5 $114.74   10.646%   $126.9552   $126.96   $126.95   $127.00  
  Purchase #6 $71.28   11.374%   $79.3874   $79.39   $79.40   $79.40  
  Purchase #7 $243.98   4.574%   $255.1396   $255.14   $255.15   $255.10  
  7 purchase totals = $796.91       $849.2100   $849.21   $849.15   $849.20