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 $183.70   12.262%   $206.2253   $206.23   $206.25   $206.20  
  Purchase #2 $140.95   4.310%   $147.0249   $147.02   $147.00   $147.00  
  Purchase #3 $48.68   8.854%   $52.9901   $52.99   $53.00   $53.00  
  Purchase #4 $111.36   13.637%   $126.5462   $126.55   $126.55   $126.50  
  Purchase #5 $249.63   5.332%   $262.9403   $262.94   $262.95   $262.90  
  Purchase #6 $36.59   11.378%   $40.7532   $40.75   $40.75   $40.80  
  Purchase #7 $193.28   3.773%   $200.5725   $200.57   $200.55   $200.60  
  7 purchase totals = $964.19       $1,037.0525   $1,037.05   $1,037.05   $1,037.00