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 $208.81   8.469%   $226.4941   $226.49   $226.50   $226.50  
  Purchase #2 $44.87   11.601%   $50.0754   $50.08   $50.10   $50.10  
  Purchase #3 $32.97   6.324%   $35.055   $35.06   $35.05   $35.10  
  Purchase #4 $124.34   9.842%   $136.5775   $136.58   $136.60   $136.60  
  Purchase #5 $81.26   7.826%   $87.6194   $87.62   $87.60   $87.60  
  Purchase #6 $87.35   7.687%   $94.0646   $94.06   $94.05   $94.10  
  Purchase #7 $218.63   3.446%   $226.164   $226.16   $226.15   $226.20  
  7 purchase totals = $798.23       $856.0500   $856.05   $856.05   $856.20