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 $163.85   13.312%   $185.6617   $185.66   $185.65   $185.70  
  Purchase #2 $149.76   8.462%   $162.4327   $162.43   $162.45   $162.40  
  Purchase #3 $15.70   3.645%   $16.2723   $16.27   $16.25   $16.30  
  Purchase #4 $157.61   7.291%   $169.1013   $169.10   $169.10   $169.10  
  Purchase #5 $190.43   7.165%   $204.0743   $204.07   $204.05   $204.10  
  Purchase #6 $84.93   3.225%   $87.669   $87.67   $87.65   $87.70  
  Purchase #7 $165.51   12.670%   $186.4801   $186.48   $186.50   $186.50  
  7 purchase totals = $927.79       $1,011.6914   $1,011.68   $1,011.65   $1,011.80