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 $147.53   4.784%   $154.5878   $154.59   $154.60   $154.60  
  Purchase #2 $231.30   3.600%   $239.6268   $239.63   $239.65   $239.60  
  Purchase #3 $232.29   11.165%   $258.2252   $258.23   $258.25   $258.20  
  Purchase #4 $36.44   4.702%   $38.1534   $38.15   $38.15   $38.20  
  Purchase #5 $222.64   13.730%   $253.2085   $253.21   $253.20   $253.20  
  Purchase #6 $36.55   11.147%   $40.6242   $40.62   $40.60   $40.60  
  Purchase #7 $76.87   5.499%   $81.0971   $81.10   $81.10   $81.10  
  7 purchase totals = $983.62       $1,065.5230   $1,065.53   $1,065.55   $1,065.50