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 $32.81   8.663%   $35.6523   $35.65   $35.65   $35.70  
  Purchase #2 $35.37   5.287%   $37.24   $37.24   $37.25   $37.20  
  Purchase #3 $203.64   10.494%   $225.01   $225.01   $225.00   $225.00  
  Purchase #4 $167.61   9.559%   $183.6318   $183.63   $183.65   $183.60  
  Purchase #5 $69.25   12.140%   $77.657   $77.66   $77.65   $77.70  
  Purchase #6 $182.89   10.338%   $201.7972   $201.80   $201.80   $201.80  
  Purchase #7 $78.25   13.432%   $88.7605   $88.76   $88.75   $88.80  
  7 purchase totals = $769.82       $849.7488   $849.75   $849.75   $849.80