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 $232.96   12.267%   $261.5372   $261.54   $261.55   $261.50  
  Purchase #2 $105.77   9.297%   $115.6034   $115.60   $115.60   $115.60  
  Purchase #3 $153.61   7.868%   $165.696   $165.70   $165.70   $165.70  
  Purchase #4 $151.62   8.225%   $164.0907   $164.09   $164.10   $164.10  
  Purchase #5 $66.65   6.355%   $70.8856   $70.89   $70.90   $70.90  
  Purchase #6 $153.88   7.576%   $165.5379   $165.54   $165.55   $165.50  
  Purchase #7 $76.35   10.313%   $84.224   $84.22   $84.20   $84.20  
  7 purchase totals = $940.84       $1,027.5748   $1,027.58   $1,027.60   $1,027.50