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 $239.39   12.607%   $269.5699   $269.57   $269.55   $269.60  
  Purchase #2 $49.79   8.641%   $54.0924   $54.09   $54.10   $54.10  
  Purchase #3 $231.64   8.742%   $251.89   $251.89   $251.90   $251.90  
  Purchase #4 $201.43   6.538%   $214.5995   $214.60   $214.60   $214.60  
  Purchase #5 $55.79   12.392%   $62.7035   $62.70   $62.70   $62.70  
  Purchase #6 $168.53   11.347%   $187.6531   $187.65   $187.65   $187.70  
  Purchase #7 $183.42   8.517%   $199.0419   $199.04   $199.05   $199.00  
  7 purchase totals = $1,129.99       $1,239.5503   $1,239.54   $1,239.55   $1,239.60