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 $222.93   10.419%   $246.1571   $246.16   $246.15   $246.20  
  Purchase #2 $238.89   9.116%   $260.6672   $260.67   $260.65   $260.70  
  Purchase #3 $14.57   6.564%   $15.5264   $15.53   $15.55   $15.50  
  Purchase #4 $231.76   7.233%   $248.5232   $248.52   $248.50   $248.50  
  Purchase #5 $248.33   13.526%   $281.9191   $281.92   $281.90   $281.90  
  Purchase #6 $114.81   7.503%   $123.4242   $123.42   $123.40   $123.40  
  Purchase #7 $34.90   10.581%   $38.5928   $38.59   $38.60   $38.60  
  7 purchase totals = $1,106.19       $1,214.8100   $1,214.81   $1,214.75   $1,214.80