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 $74.62   6.222%   $79.2629   $79.26   $79.25   $79.30  
  Purchase #2 $245.80   12.156%   $275.6794   $275.68   $275.70   $275.70  
  Purchase #3 $101.86   4.739%   $106.6871   $106.69   $106.70   $106.70  
  Purchase #4 $176.91   6.725%   $188.8072   $188.81   $188.80   $188.80  
  Purchase #5 $122.75   10.527%   $135.6719   $135.67   $135.65   $135.70  
  Purchase #6 $107.84   13.862%   $122.7888   $122.79   $122.80   $122.80  
  Purchase #7 $134.99   5.456%   $142.3551   $142.36   $142.35   $142.40  
  7 purchase totals = $964.77       $1,051.2524   $1,051.26   $1,051.25   $1,051.40