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 $73.66   13.532%   $83.6277   $83.63   $83.65   $83.60  
  Purchase #2 $215.78   11.790%   $241.2205   $241.22   $241.20   $241.20  
  Purchase #3 $242.92   11.386%   $270.5789   $270.58   $270.60   $270.60  
  Purchase #4 $231.95   13.697%   $263.7202   $263.72   $263.70   $263.70  
  Purchase #5 $42.81   7.149%   $45.8705   $45.87   $45.85   $45.90  
  Purchase #6 $227.34   11.222%   $252.8521   $252.85   $252.85   $252.90  
  Purchase #7 $172.25   5.543%   $181.7978   $181.80   $181.80   $181.80  
  7 purchase totals = $1,206.71       $1,339.6677   $1,339.67   $1,339.65   $1,339.70