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 $82.91   10.273%   $91.4273   $91.43   $91.45   $91.40  
  Purchase #2 $235.48   9.493%   $257.8341   $257.83   $257.85   $257.80  
  Purchase #3 $30.84   13.510%   $35.0065   $35.01   $35.00   $35.00  
  Purchase #4 $70.70   4.293%   $73.7352   $73.74   $73.75   $73.70  
  Purchase #5 $118.27   13.284%   $133.981   $133.98   $134.00   $134.00  
  Purchase #6 $53.35   12.635%   $60.0908   $60.09   $60.10   $60.10  
  Purchase #7 $70.66   10.768%   $78.2687   $78.27   $78.25   $78.30  
  7 purchase totals = $662.21       $730.3436   $730.35   $730.40   $730.30