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 $22.76   5.292%   $23.9645   $23.96   $23.95   $24.00  
  Purchase #2 $220.25   11.280%   $245.0942   $245.09   $245.10   $245.10  
  Purchase #3 $95.41   7.226%   $102.3043   $102.30   $102.30   $102.30  
  Purchase #4 $188.81   6.788%   $201.6264   $201.63   $201.65   $201.60  
  Purchase #5 $54.50   4.839%   $57.1373   $57.14   $57.15   $57.10  
  Purchase #6 $69.66   10.315%   $76.8454   $76.85   $76.85   $76.80  
  Purchase #7 $242.57   13.635%   $275.6444   $275.64   $275.65   $275.60  
  7 purchase totals = $893.96       $982.6165   $982.61   $982.65   $982.50