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 $245.71   7.452%   $264.0203   $264.02   $264.00   $264.00  
  Purchase #2 $68.66   7.126%   $73.5527   $73.55   $73.55   $73.60  
  Purchase #3 $142.58   10.609%   $157.7063   $157.71   $157.70   $157.70  
  Purchase #4 $140.72   7.690%   $151.5414   $151.54   $151.55   $151.50  
  Purchase #5 $124.31   10.429%   $137.2743   $137.27   $137.25   $137.30  
  Purchase #6 $133.84   4.356%   $139.6701   $139.67   $139.65   $139.70  
  Purchase #7 $10.68   10.564%   $11.8082   $11.81   $11.80   $11.80  
  7 purchase totals = $866.50       $935.5733   $935.57   $935.50   $935.60