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 $196.94   8.788%   $214.2471   $214.25   $214.25   $214.20  
  Purchase #2 $222.81   11.571%   $248.5913   $248.59   $248.60   $248.60  
  Purchase #3 $58.55   7.641%   $63.0238   $63.02   $63.00   $63.00  
  Purchase #4 $75.53   11.874%   $84.4984   $84.50   $84.50   $84.50  
  Purchase #5 $183.92   6.447%   $195.7773   $195.78   $195.80   $195.80  
  Purchase #6 $24.39   3.145%   $25.1571   $25.16   $25.15   $25.20  
  Purchase #7 $128.95   5.532%   $136.0835   $136.08   $136.10   $136.10  
  7 purchase totals = $891.09       $967.3785   $967.38   $967.40   $967.40