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 $67.47   9.270%   $73.7245   $73.72   $73.70   $73.70  
  Purchase #2 $206.75   12.602%   $232.8046   $232.80   $232.80   $232.80  
  Purchase #3 $37.69   11.337%   $41.9629   $41.96   $41.95   $42.00  
  Purchase #4 $217.42   11.715%   $242.8908   $242.89   $242.90   $242.90  
  Purchase #5 $98.63   4.443%   $103.0121   $103.01   $103.00   $103.00  
  Purchase #6 $53.41   10.379%   $58.9534   $58.95   $58.95   $59.00  
  Purchase #7 $17.48   10.169%   $19.2575   $19.26   $19.25   $19.30  
  7 purchase totals = $698.85       $772.6058   $772.59   $772.55   $772.70