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 $58.51   11.180%   $65.0514   $65.05   $65.05   $65.10  
  Purchase #2 $105.68   9.291%   $115.4987   $115.50   $115.50   $115.50  
  Purchase #3 $166.46   10.372%   $183.7252   $183.73   $183.75   $183.70  
  Purchase #4 $45.84   5.576%   $48.396   $48.40   $48.40   $48.40  
  Purchase #5 $200.42   3.105%   $206.643   $206.64   $206.65   $206.60  
  Purchase #6 $191.50   9.695%   $210.0659   $210.07   $210.05   $210.10  
  Purchase #7 $30.89   3.752%   $32.049   $32.05   $32.05   $32.00  
  7 purchase totals = $799.30       $861.4292   $861.44   $861.45   $861.40