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 $241.91   8.322%   $262.0418   $262.04   $262.05   $262.00  
  Purchase #2 $198.28   3.584%   $205.3864   $205.39   $205.40   $205.40  
  Purchase #3 $198.75   6.535%   $211.7383   $211.74   $211.75   $211.70  
  Purchase #4 $143.57   7.474%   $154.3004   $154.30   $154.30   $154.30  
  Purchase #5 $187.76   12.868%   $211.921   $211.92   $211.90   $211.90  
  Purchase #6 $207.95   12.488%   $233.9188   $233.92   $233.90   $233.90  
  Purchase #7 $73.38   3.808%   $76.1743   $76.17   $76.15   $76.20  
  7 purchase totals = $1,251.60       $1,355.4810   $1,355.48   $1,355.45   $1,355.40