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 $57.41   8.294%   $62.1716   $62.17   $62.15   $62.20  
  Purchase #2 $244.79   9.385%   $267.7635   $267.76   $267.75   $267.80  
  Purchase #3 $67.46   13.617%   $76.646   $76.65   $76.65   $76.60  
  Purchase #4 $114.69   13.314%   $129.9598   $129.96   $129.95   $130.00  
  Purchase #5 $231.47   7.537%   $248.9159   $248.92   $248.90   $248.90  
  Purchase #6 $78.52   9.246%   $85.78   $85.78   $85.80   $85.80  
  Purchase #7 $101.46   5.874%   $107.4198   $107.42   $107.40   $107.40  
  7 purchase totals = $895.80       $978.6566   $978.66   $978.60   $978.70