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 $234.92   11.146%   $261.1042   $261.10   $261.10   $261.10  
  Purchase #2 $122.92   9.535%   $134.6404   $134.64   $134.65   $134.60  
  Purchase #3 $196.73   9.561%   $215.5394   $215.54   $215.55   $215.50  
  Purchase #4 $40.77   7.296%   $43.7446   $43.74   $43.75   $43.70  
  Purchase #5 $137.39   10.757%   $152.169   $152.17   $152.15   $152.20  
  Purchase #6 $233.80   3.372%   $241.6837   $241.68   $241.70   $241.70  
  Purchase #7 $154.64   4.263%   $161.2323   $161.23   $161.25   $161.20  
  7 purchase totals = $1,121.17       $1,210.1136   $1,210.10   $1,210.15   $1,210.00