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 $84.57   13.233%   $95.7611   $95.76   $95.75   $95.80  
  Purchase #2 $90.61   8.421%   $98.2403   $98.24   $98.25   $98.20  
  Purchase #3 $60.81   12.757%   $68.5675   $68.57   $68.55   $68.60  
  Purchase #4 $199.94   11.849%   $223.6309   $223.63   $223.65   $223.60  
  Purchase #5 $19.34   9.378%   $21.1537   $21.15   $21.15   $21.20  
  Purchase #6 $116.86   5.660%   $123.4743   $123.47   $123.45   $123.50  
  Purchase #7 $226.58   8.231%   $245.2298   $245.23   $245.25   $245.20  
  7 purchase totals = $798.71       $876.0576   $876.05   $876.05   $876.10