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 $96.62   6.396%   $102.7998   $102.80   $102.80   $102.80  
  Purchase #2 $176.25   3.621%   $182.632   $182.63   $182.65   $182.60  
  Purchase #3 $54.49   5.152%   $57.2973   $57.30   $57.30   $57.30  
  Purchase #4 $60.68   3.131%   $62.5799   $62.58   $62.60   $62.60  
  Purchase #5 $248.76   5.360%   $262.0935   $262.09   $262.10   $262.10  
  Purchase #6 $87.70   3.633%   $90.8861   $90.89   $90.90   $90.90  
  Purchase #7 $16.27   7.611%   $17.5083   $17.51   $17.50   $17.50  
  7 purchase totals = $740.77       $775.7969   $775.80   $775.85   $775.80