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 $246.89   4.824%   $258.8   $258.80   $258.80   $258.80  
  Purchase #2 $22.36   12.303%   $25.111   $25.11   $25.10   $25.10  
  Purchase #3 $24.73   11.779%   $27.6429   $27.64   $27.65   $27.60  
  Purchase #4 $164.65   11.283%   $183.2275   $183.23   $183.25   $183.20  
  Purchase #5 $171.64   8.697%   $186.5675   $186.57   $186.55   $186.60  
  Purchase #6 $62.30   12.373%   $70.0084   $70.01   $70.00   $70.00  
  Purchase #7 $203.50   7.259%   $218.2721   $218.27   $218.25   $218.30  
  7 purchase totals = $896.07       $969.6294   $969.63   $969.60   $969.60