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 $196.75   4.197%   $205.0076   $205.01   $205.00   $205.00  
  Purchase #2 $191.96   7.835%   $207.0001   $207.00   $207.00   $207.00  
  Purchase #3 $227.97   4.467%   $238.1534   $238.15   $238.15   $238.20  
  Purchase #4 $186.58   11.487%   $208.0124   $208.01   $208.00   $208.00  
  Purchase #5 $57.72   3.138%   $59.5313   $59.53   $59.55   $59.50  
  Purchase #6 $203.89   13.832%   $232.0921   $232.09   $232.10   $232.10  
  Purchase #7 $90.63   4.301%   $94.528   $94.53   $94.55   $94.50  
  7 purchase totals = $1,155.50       $1,244.3249   $1,244.32   $1,244.35   $1,244.30