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 $79.26   8.592%   $86.07   $86.07   $86.05   $86.10  
  Purchase #2 $102.34   5.214%   $107.676   $107.68   $107.70   $107.70  
  Purchase #3 $231.56   12.125%   $259.6367   $259.64   $259.65   $259.60  
  Purchase #4 $140.54   12.163%   $157.6339   $157.63   $157.65   $157.60  
  Purchase #5 $244.59   8.294%   $264.8763   $264.88   $264.90   $264.90  
  Purchase #6 $236.59   12.358%   $265.8278   $265.83   $265.85   $265.80  
  Purchase #7 $214.28   12.145%   $240.3043   $240.30   $240.30   $240.30  
  7 purchase totals = $1,249.16       $1,382.0250   $1,382.03   $1,382.10   $1,382.00