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 $55.36   9.834%   $60.8041   $60.80   $60.80   $60.80  
  Purchase #2 $247.81   5.510%   $261.4643   $261.46   $261.45   $261.50  
  Purchase #3 $70.85   4.516%   $74.0496   $74.05   $74.05   $74.00  
  Purchase #4 $115.81   12.126%   $129.8531   $129.85   $129.85   $129.90  
  Purchase #5 $236.60   5.531%   $249.6863   $249.69   $249.70   $249.70  
  Purchase #6 $147.42   12.422%   $165.7325   $165.73   $165.75   $165.70  
  Purchase #7 $76.46   9.396%   $83.6442   $83.64   $83.65   $83.60  
  7 purchase totals = $950.31       $1,025.2341   $1,025.22   $1,025.25   $1,025.20