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 $135.83   11.621%   $151.6148   $151.61   $151.60   $151.60  
  Purchase #2 $57.94   7.348%   $62.1974   $62.20   $62.20   $62.20  
  Purchase #3 $135.36   3.358%   $139.9054   $139.91   $139.90   $139.90  
  Purchase #4 $26.63   5.693%   $28.146   $28.15   $28.15   $28.10  
  Purchase #5 $237.70   12.438%   $267.2651   $267.27   $267.25   $267.30  
  Purchase #6 $169.76   12.183%   $190.4419   $190.44   $190.45   $190.40  
  Purchase #7 $184.80   6.284%   $196.4128   $196.41   $196.40   $196.40  
  7 purchase totals = $948.02       $1,035.9834   $1,035.99   $1,035.95   $1,035.90